Beyond Linux: a tour of free operating systems

Almost every computer you touch runs a descendant of UNIX or of Windows NT. It is easy to conclude that the question of how to build an operating system is settled. It is not — it is just that the alternatives rarely get in front of anyone. Here are the ones worth booting.

Haiku — the one that feels finished

BeOS was a commercial desktop OS from the mid-90s built around media work, with a responsiveness that people who used it still talk about. It died commercially; Haiku is the open-source project that has spent two decades rebuilding it. It is not a tribute — it is a working, coherent desktop with a filesystem that behaves like a database and a design where everything was decided by the same people at the same time. Of everything on this list, Haiku is the one most likely to make you wonder why your computer does not feel like this.

ReactOS — Windows without Windows

ReactOS is an attempt to build an operating system binary-compatible with Windows: same driver model, same application interface, entirely independent implementation. Not a Linux distribution with a compatibility layer bolted on — a from-scratch NT-style kernel. It is the answer to "could Windows have been free software?", and booting it is faintly disorienting: the desktop is familiar down to the control panel, and none of it is Microsoft's.

The BSDs — the other UNIX lineage

Linux is a kernel that a distribution assembles a system around. The BSDs are complete operating systems developed as a single unit — kernel, userland and documentation by the same project, which shows in how consistent they feel.

• FreeBSD — the pragmatic one, and the reason a lot of the internet stays up. Netflix serves video from it.
• OpenBSD — security taken to the point of obsession. It gave the world OpenSSH, and audits its own code line by line.
• NetBSD — built on the premise that one clean codebase should run on everything, which it very nearly does.
• 386BSD — the 1992 ancestor the other three descend from. Historically, not practically, interesting.

Plan 9 — UNIX's authors trying again

The people who created UNIX at Bell Labs eventually decided they could do better, and built Plan 9. The idea UNIX half-committed to — that everything is a file — is taken completely seriously here: your network connections are files, your window system is a filesystem, and remote resources are mounted into your namespace so transparently that using another machine's hardware is indistinguishable from using your own.

It never displaced UNIX, but its ideas leaked everywhere — UTF-8 was invented for it, and container namespaces are Plan 9's per-process namespaces rediscovered. 9front is the maintained fork; be warned that the interface is mouse-driven in a way that will feel wrong for about twenty minutes.

Redox — what if we started today?

A microkernel operating system written entirely in Rust, with its own filesystem, its own C library and a graphical desktop. The premise is that most serious security bugs come from memory errors, and that a system written in a language which prevents them at compile time would simply not have that category of bug. Redox is the most serious attempt to test that premise at the scale of a whole OS.

SerenityOS — built in public, from nothing

One person started writing an operating system on video and did not stop: kernel, compiler, browser engine, IDE, all from scratch, with the deliberate look of a late-90s Unix workstation. It has no reuse of existing components as a matter of principle. What makes it remarkable is not the aesthetic but that the whole thing was built in the open, one recorded session at a time.

Where to start

If you have ten minutes, boot Haiku — it is the one that most rewards a short visit. If you have an afternoon and a taste for being confused productively, boot 9front. If you want to see something you cannot quite believe is not Windows, boot ReactOS.