Gentoo Linux

I used Gentoo Linux for more than a decade and even though I've since moved onto Arch, I still love it.

Gentoo is what you use when you've got a very particular setup in mind: maybe it's an odd piece of hardware (I installed it on a Sheevaplug that ran a vending machine years ago), or maybe you want to build a machine capable of cross compiling a bajillion other things for different architectures and plug said machine into a swarm. Gentoo is great for that: maximum customisability and total control of your operating system.