Linux

FreeBSD

 Nice to hear someone echo my own thoughts on the subject:

Why use FreeBSD? Maybe I’m just getting old, but it’s nice to use an operating system that didn’t spawn a billion-dollar anti-malware industry through frequent security failings, where you can choose the interface you like and reasonably expect it to stay that way instead of being forced into the design fad du jour, where you don’t have to argue about the init system being replaced two times in the same decade, and whose key organizations don’t collectively kowtow to Microsoft when convenient. - Cool Trainer dot org

The rest of the page goes into glorious (horrible) technical detail on I don't want to know what, but the intro is great.

BSD in FreeBSD is Berkeley Software Distribution
Via Detroit Steve