When you say “open source,” your mind probably immediately goes to Linux. And it’s true — Linux has been the poster child of open source, running everything from smartphones to supercomputers.
But here’s a little secret: Linux isn’t the only open source OS out there. In fact, there’s a whole world of alternative operating systems — many of which predate Linux — that offer their own unique take on computing.
Whether you’re a curious tinkerer, a nostalgic gamer, or just someone fascinated by digital history, here are 9 open source operating systems worth exploring (and none of them are Linux!).
9. Plan 9 from Bell Labs
If you’ve never heard of Plan 9, you’re not alone — but it’s a true gem for OS geeks. Born from the legendary minds behind Unix, Plan 9 pushed the “everything is a file” philosophy even further, blending local and remote systems into a seamless experience.
Its objective? To create a real distributed OS, with workstations serving as terminals to compute and file servers. Though it never conquered the world — partly thanks to the reign of Windows, Unix, then Linux — Plan 9’s concepts continue to shape OS designs today. And yes — you can still download and execute it today.
8. Haiku
Remember BeOS? Chances are, you smiled just seeing that. BeOS was an innovative ’90s multimedia OS centered on speed, efficiency, and multicore support, all before that was normal.
Though BeOS ultimately lost out, its legacy exists in Haiku — a contemporary open source reimagination of BeOS. Haiku is light, quick, and designed for work creation — a love letter to a time when operating systems had visions of a different sort.
7. Minix
Discuss influence — had Minix not existed, there may not have been a Linux. Originally constructed as an educational device by Andrew Tanenbaum, Minix demonstrated the microkernel design and was an inspiration to one young Finnish student by the name of Linus Torvalds.
While Linux later commanded the spotlight, Minix developed into a powerful, super-reliable OS in its own right, and a fully open-source one at that. To glimpse where open-source OS history started all those years ago, here’s a good place to begin.
6. HelenOS
HelenOS is a microkernel-based project again — but what makes it special is its charmingly retrofuturistic look, reminiscent of Windows 3.1 and 95.
Although still an R&D project (and not quite ready to become your everyday car), HelenOS provides an interesting playground for anyone who wants to try out alternative process management and OS design. And besides, it’s simply enjoyable to poke around in.
5. AROS
Amiga fans — this one’s for you. AROS (AROS Research Operating System) exists to reimagine and reinvent the classic AmigaOS experience.
And the best part? AROS runs on a wide variety of hardware, from classic Amigas to modern PCs. Whether you’re revisiting your youth or discovering Amiga-style computing for the first time, AROS delivers that distinctive charm.
4. ReactOS
If AROS is the Amiga’s spiritual successor, ReactOS is an ambitious attempt to recreate Windows — but fully open source.
Desperate to be compatible with Windows NT (and mimicking the look and feel of old Windows 9.x), ReactOS has an uphill battle due to Microsoft’s changing APIs and legal issues. But in spite of it all, it’s usable and a fun project — and yes, even includes Solitaire.
3. FreeDOS
It’s old-fashioned now, but MS-DOS dominated the PC scene back then. These days, FreeDOS maintains the tradition as an open source DOS clone.
Why use it in 2025? For nostalgia, perhaps — but also for retro gaming, BIOS flashing, or running ultra-simple embedded systems. If you learned to type C:\> at a command prompt as a kid, FreeDOS is a fun flashback.
2. GNU Hurd
Prior to the Linux kernel taking center stage, the GNU Project envisioned having its own completely free kernel — GNU Hurd. Hurd, based on the Mach microkernel, would serve to drive a whole open source OS.
It’s been an understandably slow (if one might use that word) going, but Hurd is still a fascinating experiment for tinkerers and dreamers alike. Though not yet production-capable, you can experiment with it using Debian GNU/Hurd — if you’re feeling adventurous.
1. The BSDs
Last but not least, no list of non-Linux open source operating systems would be complete without mentioning the BSD family. Founded on Berkeley Software Distribution (BSD) — a cutting-edge Unix variant — the BSDs of today are strong, mature, and ubiquitous.
FreeBSD is well-known for its excellent ZFS support and runs most of Netflix’s CDN.
NetBSD will run on basically anything — even toasters.
OpenBSD is lauded for its security-centric approach.
DragonFlyBSD introduces innovative concepts such as the HAMMER2 filesystem and virtual kernels.
The BSDs might not make headlines as Linux does, but they humbly power a lot of the contemporary web.
Final Thoughts
It’s easy to assume Linux is the whole world of open source operating systems — but as this list indicates, there’s a whole galaxy of interesting alternatives awaiting.
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