Five? Wow, I think I only knew one.
I've completely forgotten about this! It was that era when there was only a few games on Linux, most of them open-sources. So you'd see them a lot in programming schools: Teeworlds, FreeCiv, Wormux, Tenka Cho games, and Chicken Invaders.

Classics.
I also remember how we were excited on the first Humble Indie Bundle.
“Guys! There's a website selling a bunch of great indie games on Linux! And they're totally DRM free! Oh, and also, you can pay what you want.” Crazy.
Then when you looked at the students' screens, you would see World of Goo, Aquaria, Gish, Penumbra, then Braid, revenge of the Titans… It's amazing how in only two years, getting games ported to Linux has become common. Not still the norm, but still enough to have a lot of games to play.
And so we don't talk as much as we did of those free games. There's isn't anymore the need to share them, since we don't really lack games now (there's a Linux client for Steam omg) (even an OS, maaaan). They were pretty cool though.
Windows users may had all the fancy AAA games, we had Chicken Invaders and Teeworlds !
(Sure, they were available on Windows as well, but whatever)