Fair question. It seems the author got distracted when writing the description.
Or maybe there's some history behind it. Like there where 3 forums at some point: Windows, Apple and *nix. But someone noticed there are other OSes as well, so they just changed the title.
Also, what about proprietary software run on Linux? Where should we discuss it?
It's not exactly a small or exotic list, since it includes Opera, Dropbox, Slack, Steam and long list of paid software available on Linux?