What is free and open source software?

All of the free and open source software listed below is available free of charge. In other words "free, as in free lunch". In addition, much of the following software is "free, as in free speech". These two concepts, although distinct, are often confused. For an in-depth discussion of free and open source software see this Wikipedia article.

Free CD/DVD writing software

• Burn for Mac
  Simple yet advanced burning for Apple OS X.
• Express Burn for Mac
  Create and record audio and data CDs and DVDs.

Free email clients and calendaring

• Mozilla Lightning
  Lightning brings calendaring to the popular email client Mozilla Thunderbird. Lightning is tightly integrated with Thunderbird, allowing it to easily perform email-related calendaring tasks.
• Mozilla Thunderbird
  Get the acclaimed email client from Mozilla. Versions of Thunderbird are available for Apple macOS, Microsoft Windows and GNU/Linux.

Free file archiving and compression

• 7-Zip
  A file archiver with a high compression ratio. Available for Microsoft Windows.
• 7zX
  7zX is a file archiver with high compression ratio. Available for Apple macOS.

Free file creation, editing and viewing

• AbiWord
  AbiWord is a free word processing program similar to Microsoft Word. Versions are available for Microsoft Windows, Apple macOS and GNU/Linux.
• Adobe Flash Player
  Adobe no longer supports Flash Player and strongly recommends all users immediately uninstall Flash Player to help protect their systems.
• Adobe Reader
  For viewing Adobe Acrobat PDF files. Versions are available for Apple macOS, Microsoft Windows and GNU/Linux.
• Apache OpenOffice
  "The Free and Open Productivity Suite." If you are using an unlicenced copy of Microsoft Office on your Windows computer and want to clear your conscience then try switching to OpenOffice - you'll probably love it. If you have installed OpenOffice then you should possibly also install Java listed below.
• Audacity
  For recording and editing sounds. Versions are available for Apple macOS, Microsoft Windows and GNU/Linux.
• Blender
  A 3D graphics creation program for Apple macOS, Microsoft Windows, GNU/Linux and FreeBSD.
• CutePDF Writer
  Create professional quality PDF files from almost any printable document. Requires Microsoft Windows.
• GIMP
  For photo retouching, image composition and image authoring. GIMP is written and developed under X11 on UNIX platforms but basically the same code also runs on Microsoft Windows and Apple macOS.
• LibreOffice
  LibreOffice is a powerful office suite – its clean interface and feature-rich tools help you unleash your creativity and enhance your productivity. LibreOffice includes several applications that make it the most powerful free and open source office suite on the market.
• NeoOffice
  Based on Apache OpenOffice, NeoOffice is a fully-featured set of office applications (including word processing, spreadsheet, presentation, and drawing programs) for Apple macOS.
• PDFCreator
  PDFCreator easily creates PDFs from any Windows program. Use it like a printer in any Windows application.
• Scribus
  Scribus is an open-source program that brings award-winning professional page layout to GNU/Linux, Unix, Apple macOS, OS/2 and Windows desktops with a combination of "press-ready" output and new approaches to page layout. Underneath the modern and user friendly interface, Scribus supports professional publishing features, such as CMYK colour, separations, ICC colour management and versatile PDF creation.

Free FTP software

• Core FTP
  This free, secure FTP client for Microsoft Windows gives you a fast, easy, reliable way to update and maintain your website via FTP.
• Cyberduck
  With an easy to use interface, connect to FTP (File Transfer Protocol), SFTP (SSH Secure File Transfer), WebDAV (Web-based Distributed Authoring and Versioning), Amazon S3, Google Cloud Storage, Microsoft Azure, Rackspace Cloud Files and even Google Docs. Versions are available for Apple macOS and Microsoft Windows.
• FileZilla
  Both a client and a server are available. FileZilla is open source software distributed free of charge under the terms of the GNU General Public License. Versions are available for Apple macOS, Microsoft Windows and GNU/Linux.
• WinSCP
  An open source free SFTP client and FTP client for Microsoft Windows.

Free firewall appliance software

• SmoothWall Express
  An open-source firewall that includes its own security-hardened GNU/Linux operating system and an easy-to-use web interface. The SmoothWall GPL project was founded in the summer of 2000 by Lawrence Manning (Principle Code Author) and Richard Morrell (Project Manager). Their goal was to create a GNU/Linux distribution that could convert a redundant PC into a hardened internet firewall device.

Free software from Apple

• Apple Downloads
  Lots of free downloads directly from Apple to enhance your Mac, PC, iPhone and iPad.

Free media players

• VLC media player
  A cross-platform media player and streaming server.

Free operating systems

• CentOS
  CentOS is an Enterprise-class GNU/Linux Distribution derived from sources freely provided to the public by a prominent North American Enterprise GNU/Linux vendor. CentOS conforms fully with the upstream vendors redistribution policy and aims to be 100% binary compatible.
• ClearOS
  ClearOS is an operating system for your Server, Network, and Gateway systems. It is designed for homes, small to medium businesses, and distributed environments. ClearOS is commonly known as the Next Generation Small Business Server, while including indispensable Gateway and Networking functionality. It delivers a powerful IT solution with an elegant user interface that is completely web-based. Simply put, ClearOS is the new way of delivering IT.
• Debian GNU/Linux
  Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run. Debian uses the GNU/Linux kernel (the core of an operating system), but most of the basic OS tools come from the GNU project; hence the name GNU/Linux. Debian GNU/Linux provides more than a pure OS: it comes with over 25000 packages, precompiled software bundled up in a nice format for easy installation on your machine. Debian is available for Alpha, AMD64, ARM, HP PA-RISC, Intel x86, Intel IA64, MIPS, MIPSEL, PowerPC, IBM S/390 and SPARC computer architectures. It is the solid base on which many other GNU/Linux distributions arebuilt including Ubuntu and GNU/Linux Mint listed elsewhere on this page.
• DragonFly BSD
  DragonFly belongs to the same class of operating systems as other BSD-derived systems and Linux. It is based on the same UNIX ideals and APIs and shares ancestor code with other BSD operating systems. DragonFly provides an opportunity for the BSD base to grow in an entirely different direction from the one taken in the FreeBSD, NetBSD, and OpenBSD series.
• Fedora
  Fedora is a GNU/Linux-based operating system that showcases the latest in free and open source software. Fedora is always free for anyone to use, modify, and distribute. It is built by people across the globe who work together as a community: the Fedora Project. The Fedora Project is open and anyone is welcome to join.
• FreeBSD
  FreeBSD is an advanced operating system for modern server, desktop, and embedded computer platforms. FreeBSD's code base has undergone over thirty years of continuous development, improvement, and optimization.
• FreeDOS
  FreeDOS is a free DOS-compatible operating system that can be used to play games, run legacy software, or support embedded systems. FreeDOS is basically like the old MS-DOS, but better!
• FreeNAS
  FreeNAS is an Open Source Storage Platform based on FreeBSD and supports sharing across Windows, Apple, and UNIX-like systems. FreeNAS uses a custom version of FreeBSD and a web-based interface to provide a fully-featured Network-Attached Storage (NAS) environment. FreeNAS offers software-based storage and backup solutions for a variety of applications, from home to enterprise.
• Kali Linux
  Kali Linux is an open source project that is maintained and funded by Offensive Security, a provider of world-class information security training and penetration testing services.
• Linux Mint
  Linux Mint is an Ubuntu-based GNU/Linux distribution whose goal is to provide a more complete out-of-the-box experience by including browser plugins, media codecs, support for DVD playback, Java and other components. It is compatible with Ubuntu software repositories.
• Mageia
  Mageia is a GNU/Linux-based, Free Software operating system. It is a community project, supported by a nonprofit organisation of elected contributors.
• MX Linux
  MX Linux is a cooperative venture between the antiX and former MEPIS communities, using the best tools and talents from each distro. It is a midweight OS designed to combine an elegant and efficient desktop with simple configuration, high stability, solid performance and medium-sized footprint.
• NetBSD
  NetBSD is a free, secure, and highly portable Unix-like Open Source operating system available for many platforms, from 64-bit Opteron machines and desktop systems to handheld and embedded devices.
• NethServer
  NethServer is an operating system for Linux enthusiasts, designed for small offices and medium enterprises. It is based on CentOS/RHEL, a widespread and popular server distribution, trusted by routine security updates, and rock solid stability.
• OpenBSD
  The OpenBSD project produces a free, multi-platform 4.4BSD-based Unix-like operating system.
• openSUSE
  The openSUSE project is a worldwide community program sponsored by Novell that promotes the use of GNU/Linux everywhere. The program provides free and easy access to openSUSE. Here you can find and join a community of users and developers, who all have the same goal in mind - to create and distribute the world's most usable GNU/Linux.
• Tomato Firmware
  Tomato Firmware is a free HyperWRT-based, GNU/Linux core firmware distribution for several wireless routers, most notably the Linksys WRT54G (including the WRT54GL and WRT54GS), Buffalo AirStation and Asus Routers.
• Ubuntu
  A complete GNU/Linux-based operating system, freely available with both community and professional support. Ubuntu GNU/Linux is available in both desktop and server editions and supports various computer architectures. Free downloads are available for Ubuntu GNU/Linux. A copy of the Ubuntu Pocket Guide and Reference is available here.
  
  There are GNU/Linux distributions available which are derived from Ubuntu, changing it in various ways. These distributions include:
  • elementary OS
    elementary OS is a free replacement for Windows on the PC and OS X on the Mac. It comes with what you'd expect, like a fast web browser and an app store with thousands of apps. Plus some things you may not expect, like free updates and no known viruses;
  • Kubuntu
    Kubuntu is an operating system built by a worldwide community of developers, testers, supporters and translators;
  • Linux Lite
    Linux Lite is a GNU/Linux distribution, based on Debian and Ubuntu. The purpose of Linux Lite is to introduce Windows users to Linux;
  • Lubuntu
    Lubuntu is a faster, more lightweight and energy saving variant of Ubuntu using LXDE, the Lightweight X11 Desktop Environment;
  • Trisquel
    Trisquel is a fully free GNU/Linux based operating system for home users, small enterprises and educational centers;
  • Ubuntu MATE
    Ubuntu MATE is a stable, easy-to-use operating system with a configurable desktop environment. Ideal for those who want the most out of their desktops, laptops and netbooks and prefer a traditional desktop metaphor. With modest hardware requirements it is suitable for modern workstations and older hardware alike.
  • Xubuntu
    Xubuntu is a complete GNU/Linux based operating system with an Ubuntu base. It is lighter on system requirements and tends to be more efficient than Ubuntu with GNOME or KDE, since it uses the Xfce Desktop environment, which makes it ideal for old or low-end machines, thin-client networks, or for those who would like to get more performance out of their hardware.
  • Zorin OS
    Zorin OS is a multi-functional operating system designed specifically for newcomers to Linux. It's based on Ubuntu Linux, so you can rely on it for rock-solid performance, dependability and support. It features our unique Look Changer program created exclusively for Zorin OS. It allows you to change the user interface at the touch of a button. Other unique programs include Background Plus, Web Browser Manager and more. Zorin OS gives you more flexibility. It allows you to use Zorin OS alongside your current operating system and run Microsoft Windows programs in Zorin OS with the help of WINE and PlayOnLinux.
• Ubuntu Pocket Guide and Reference
  Written by award-winning author Keir Thomas, Ubuntu Pocket Guide and Reference is a totally unique and concise guide for everyday Ubuntu use. It is the world's most popular and widely-read Ubuntu book!

Free support software

• Java
  Java software allows you to run applications called "applets" that are written in the Java programming language. Versions of Java available for Apple macOS, Microsoft Windows and GNU/Linux.
• PuTTY
  A free Telnet/SSH client for Microsoft Windows.

Free telephony software

• Skype
  Make phone, text and video calls from your computer. It's free to other people on Skype and cheap to phones and mobiles across the world. Available for Apple macOS, Microsoft Windows and GNU/Linux.

Free website authoring

• Drupal
  Drupal is a free software package that allows an individual or a community of users to easily publish, manage and organize a wide variety of content on a website.
• e107
  A content management system written in PHP and using the popular open source MySQL database system for content storage. It's completely free, totally customisable and in constant development.
• Joomla!
  Joomla! is one of the most powerful Open Source Content Management Systems on the planet. It is used all over the world for everything from simple websites to complex corporate applications.Joomla! is easy to install, simple to manage, and reliable.
• Nvu
  A complete Web Authoring System for GNU/Linux desktop users as well as Microsoft Windows and Apple macOS users to rival programs like FrontPage and Dreamweaver.
• Open Source Web Design
  To put it simply, Open Source Web Design is a collection of web designs submitted by the community that anyone can download free of charge!The Open Source Web Design project was founded in September 2000 by Francis J. Skettino. The goal was to provide the Open Source community with quality web designs to help get people's projects on the web in a way that is both organized and good looking. From personal blogs to content management systems and fully fledged businesses, OSWD has been providing free web designs for years.
• Serendipity
  Serendipity is a PHP-powered weblog application which gives the user an easy way to maintain an online diary, weblog or even a complete homepage. While the default package is designed for the casual blogger, Serendipity offers a flexible, expandable and easy-to-use framework with the power for professional applications.
• TYPO3
  TYPO3 is a free Open Source content management system for enterprise purposes on the web and in intranets. It offers full flexibility and extendability while featuring an accomplished set of ready-made interfaces, functions and modules.
• WordPress
  WordPress is a state-of-the-art publishing platform with a focus on aesthetics, web standards, and usability.

Free web browsers

• Brave
  The new Brave browser blocks ads and trackers that slow you down and invade your privacy. Versions are available for Apple macOS, Microsoft Windows and GNU/Linux.
• Google Chrome
  Google Chrome is a browser that combines a minimal design with sophisticated technology to make the web faster, safer, and easier. Versions are available for Apple macOS, Microsoft Windows and GNU/Linux.
• Chromium
  Chromium is a free and open-source web browser project, mainly developed and maintained by Google. This codebase provides the vast majority of code for the Google Chrome browser, which is proprietary software and has some additional features. The Chromium codebase is widely used. Versions are available for Apple macOS, Microsoft Windows and GNU/Linux.
• Microsoft Edge
  World-class performance with more privacy, more productivity, and more value while you browse.
• Mozilla Firefox
  The award-winning Web browser is better than ever. Faster, safer, and easy to use, Firefox delivers a better Web experience.
• Opera
  Opera delivers robust security and a far-richer feature set than any other Web browser.
• SeaMonkey
  Not just a Web browser but a suite of Internet tools powered by Mozilla, it includes a browser, a client for mail and newsgroups and an HTML editor. Versions are available for Apple macOS, Microsoft Windows and GNU/Linux.

Free virus protection for Mac

• Avira
  Mac malware is now a reality, but the days of worry-free Mac computing are far from over. Install Avira Free Mac Security and postpone the era of Mac viruses.
• ClamXAV
  A free virus checker for Apple macOS.
• Norton Security
  Norton Security Premium offers comprehensive protection.
• Free Sophos antivirus Home Edition
  Protect all the computers in your home with the free Sophos Home.

Free Windows spyware and virus protection

• Advanced SystemCare Free
  Advanced SystemCare Free has a one-click approach to help protect, repair, clean, and optimize your PC. With millions of downloads since 2006, this fantastic, award-winning, free PC repair software is a "must-have" tool for your computer. 100% safe with no adware, spyware, or viruses; a PC maintenance program that's incredibly easy to use.
• AVG Free Edition
  The free version of AVG antivirus for Microsoft Windows.
• Avira AntiVir
  Free antivirus software for private and individual users of Microsoft Windows.
• ClamWin
  Free antivirus for Microsoft Windows.
• Microsoft Security Essentials
  Microsoft Security Essentials provides real-time protection for your home or small business PC that guards against viruses, spyware, and other malicious software.
• Free Sophos antivirus Home Edition
  Protect all the computers in your home with the free Sophos Home.

Free virtual machines

• VirtualBox
  VirtualBox is a general-purpose full virtualizer for x86 hardware. Targeted at server, desktop and embedded use, it is now the only professional-quality virtualization solution that is also Open Source Software.

Even more free and open source software

• Christopher Smart's blog
  Just another Linux geek.
• Guru99 tutorials library
  A totally new kind of learning experience.
• Guru99 Kali Linux Tutorial
  Kali Linux is a Security Distribution of Linux specifically designed for digital forensics and penetration testing.