Free Alternative Operating Systems

Free and Open Source OSes / Platforms

Free Alternative Operating Systems

Tired of Windows, Mac OS X, Linux or whatever operating system that you're currently using on your computer, and feel like trying something new? Or perhaps you want to test the cutting edge in operating system design or find out what the platform of the future is going to be like. Or you may simply want to try out a system that your friends are using to see whether you can use it for your computer. This page lists a variety of free operating systems available that you can download and install on your computer. Many of the systems are also open source so you can also tinker with the system, find out how it works, and learn from it.

Note that you do not actually have to have an unused computer to install any of these systems. An easy way is to install one or more of these systems into a "virtual machine", which can run on your existing system. This allows you to try out the system without forgoing the comforts and convenience of your existing system (be it Windows, Mac, Linux or otherwise). You can get a virtual machine or emulator from the Free x86 / PC Emulators and Virtual Machines page. An alternative method, albeit less convenient, is to install the new system in another partition on your hard disk, side-by-side with your existing system, in something known as a dual-boot (or multi-boot) configuration. This has the advantage of allowing you to experience the actual speed of the operating system (which you won't get in a virtual machine). If you want to do this, you may be interested in getting a partitioning utility to create the new partition (and perhaps resize your existing partition to make space) from the Free Partitioning Software page. If you are trying an OS that doesn't already come with its own boot manager, you may also want to download a multi-boot manager from the Free Boot Managers and Multi-Boot Loaders page.

As always, you should back up your computer before you mess with it in such a drastic way (whether you take the virtual machine or the dual-boot route). Free backup software can be found on the Free Hard Disk Backup and Restore, Hard Disk Image and Cloning Utilities page.

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Free Alternative Operating Systems

Qubes OS

Qubes OS is an operating system designed with security foremost in mind. It does this by using "security by isolation" where not only are programs isolated from each other, but even some system components (like the networking and storage subsystems) are also sandboxed. This is done with the aid of virtualisation ("virtualization"). This open source system is based on Xen, Linux and the X Window system. At the time this entry was written, the software is still under development (that is, it's not ready for production use).

Plan 9

Plan 9 is a research system originally designed by Ken Thompson, Rob Pike, Dave Presotto and Phil Winterbottom. Unlike many other operating systems, all resources in Plan 9 are accessed like files in a hierarchical file system. While Unix-type systems already provided such an encapsulation, with many devices mapped to the file system, Plan 9 goes even further, so that even things like the network and user interface window are also accessed in this way, through a standard protocol called "9P". The operating system can also (optionally) work as a distributed system, with its components distributed among different hardware platforms. As of 23 March 2021, it is released under the MIT License.

Chromium OS (Google Chrome OS)

Chromium OS is the open source operating system from Google that will form the basis of Google's Chrome OS. It uses a modified Linux kernel and is primarily intended for devices like netbooks. As such, the main user interface is probably the web browser, with most (if not all) applications that a user runs being web applications. Although the system is still under development, the source code is already available for you to download and play with.


MINIX is a POSIX compliant operating system for the PC (although ports to Xscale and PowerPC are supposed to be underway) with a microkernel architecture (where the operating system core, or kernel, does the bare mininum and everything else is implemented separately [in user space]). It has TCP/IP networking, supports the X Window system, runs the GNU compiler tools and many other Unix utilities, has device drivers that run as user processes, etc. The system is released as open source.


This is a complete software stack for mobile devices comprising the base operating system as well as applications that run on it. The operating system itself is a fork of the Linux kernel, while the software in the stack are Java applications. The system runs on ARM processors, although there is apparently also an x86 version. Android is currently used on many devices including smartphones and netbooks.


This is an x86 32-bit operating system written completely in assembly language, that is optimised ("optimized" in US English) for speed. Only a single process can execute at a time, although that process can have multiple threads. Since the process runs at ring 0, it has complete access to all hardware. The system (by design) does not support virtual memory (paging) nor indeed even provide any memory allocation API (other than functions to get the conventional and extended memory size and the top of usable memory); your program manages memory itself. It does however have a TCP/IP stack (for Internet support), support for some Ethernet cards, comes with an integrated development environment (IDE), and a basic user interface. The entire OS is very small, and (at the time I write this) can apparently fit into less than 64KB of memory. (The entire download file is also very small: about 8.8 MB at the time I checked it.) You don't have to install to your hard disk if you only want to try it: the OS can be booted from a USB flash drive, a floppy disk or a CD.


Linux began its life as a Unix-clone, but has over time become the dominant Unix-type platform in use today (at the time I write this). Created by Linus Torvalds in 1991, it is commonly found on servers, but can also be found in embedded devices, desktop computers, and so on. The core of the system, the Linux kernel, is licensed under the GNU General Public License. As distributed, Linux is packaged differently by a variety of vendors, with each vendor adding its own software mix and external visual appearance to the overall package. These packages are called "distributions" in the Linux world, and you can find a list of the most popular distributions from the above link. Instead of installing a distribution, you can also download a Linux Live-CD which allows you to boot from the CD/DVD into a complete Linux system without installing anything.

BSD-based Systems: FreeBSD, OpenBSD, NetBSD, Darwin

BSD started out as a derivative of the original AT&T Unix system, although today, the modern open source BSD-based systems no longer has any AT&T code. It is released under a permissive BSD licence. See the page linked-to above for more details as well as links to the various free BSD systems.

BeOS and Clones

BeOS is an OS from the 1990s designed for its own hardware that has since been ported to the PC. It was optimized for work with digital media and has many modern operating system features. Although the original BeOS is no longer being maintained, an open source project called Haiku continues its development. See the page linked to above for details.

MS-DOS and Clones: FreeDOS, DR-DOS, IBM PC-DOS

MSDOS, PC-DOS, and its clones, DR-DOS and FreeDOS, were operating systems widely used on PCs in the 1980s and early 1990s. The last I checked, the open source equivalent, FreeDOS, is still under development and runs fine on modern hardware.

Windows Clones and Emulation Layers

Windows clones and emulation layers let you run Windows programs without having to buy a copy of Windows. See the page linked-to for more details.

Singularity Project

[Update: this source archive will be shut down after 1 July 2021. The project's official site may still exist, although it does not provide any download links.]
This is a research project by Microsoft intended to use the advances in software engineering in the design and implementation of an operating system. The operating system runs every program, device driver and system extension in its own isolated space, which they call Software Isolated Process (SIP). Programs cannot share memory or even modify their own code. The aim is to make the system more reliable and robust. The research development kit (RDK) for Singularity contains the source code, build tools, test suites and documentation for the project. It is licensed for academic non-commercial use only (read their licence for the details).

Symbian (no longer available)

Symbian, from Nokia, is an operating system for smartphones and other mobile devices. It uses a microkernel architecture, has real-time features, supports pre-emptive multitasking and memory protection, and is designed with the philosophy that resources are scarce. It is a popular mobile operating system in current (at the time this was written) use. Update (28 November 2010): The Symbian website will apparently be closed on 17 December 2010. If you want to download the source code, you'll have to do it before that date. Update (2011): Well, I just checked, and it's no longer available.

OpenSolaris (no longer available)

OpenSolaris is a Unix derivative, based on Solaris, which is in turn based on Unix System V Release 4. It runs on the x86 family of processors as well as SPARC (UltraSPARC, SPARC64). The majority of the code is released as open source under the Common Development and Distribution License (CDDL), although there are apparently also some binary-only components released under the OpenSolaris Binary License. Update (August 2010): with the purchase of Sun by Oracle, and consequently Solaris, it looks like OpenSolaris will no longer be updated or maintained. Update (25 Mar 2013): Another one bites the dust. It looks like OpenSolaris is no longer available.

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