(computing, Internet) Unix and various other similar and/or compatible operating systems.

present participle of nix

simple past tense and past participle of nix

(dated, slang) it doesn't matter; no worries / 1983, Ian Skidmore, Forgive Us Our Press Passes, →ISBN, page 21: / 'Nice people, are they?I shouldn't think so.Aw, well. Mox nix. Want some of this rice?'

(dated, slang) unimportant, irrelevant