In order for an operating system to be truly geeky, it has to fulfill certain requirements.

1. Must not be Windows.
2. Must not be Mac.
3. Must have a huge learning curve and take months to master.
4. Must be ugly. A truly geeky OS isn’t pretty. The GUI should only be the absolute bare minimum in order to get the job done.
5. Must have the vast majority of command functions done via CLI. And if you don’t know what CLI is, then darn it, you’re just not geeky enough to use it.

Some of you may have guessed FreeBSD. Good guess, but wrong.

You also might have guessed old-time computing from the 8-bit or 16-bit era. Also wrong.

The geekiest OS next to having an IBM S/390 mainframe in your house is Plan 9.

What is Plan 9?

Plan 9 is intended to be a successor to UNIX, coded originally at Bell Labs, the people who brought you the original UNIX.

If you know UNIX at all, you will have some familiarity with Plan 9. On the surface, UNIX and Plan 9 appear to act the same, but the "guts" of how it works is distinctively different. You can read more about it on Wikipedia’s Plan 9 Design Concepts section. You can also read Plan 9′s docs directly.

What does Plan 9 look like?

Like something from 1988:

The bunny seen is called Glenda, the Plan 9 mascot. Linux has a penguin; Plan 9 has a bunny.

What makes Plan 9 so geeky?

The geeky nature comes from the fact that even if you already know UNIX, you’ll have to learn it all over again when you start using Plan 9. And even if you’re able to make do with the way it works, getting things done will be a challenge at best. Is it a worthy challenge? That’s up for you to decide.

What can you do with Plan 9?

You could use it for its intended purpose, that being for research to see what the next UNIX could be like. But as far as using it as your daily work OS, well.. probably not. You’d be better off with the penguin for day-to-day computing instead of the bunny.