@email@example.com Xonotic; Chromium B.S.U; FreeCiv; OpenTTD; 0 A.D.
That's a few of the top of my head.
@eliasr OpenTTD, Glest, Tuxracer, Chromium B.S.U., Torcs
@eliasr supertux2, supertuxkart
@eliasr that was going to be my recommendation, specifically Nodecore if they like to tinker. It's a whole different game.
@eliasr 1) frogatto is a fun 2D side scroller; 2) (extreme) tux racer is a fun downhill racing game; 3) neverputt is a challenging 3D putting game ; 4) Super Tux Cart is like Mario Kart; 5) Pioneers is computer version of the board Settlers of Catan.
@eliasr sdlpop, jumpnbump, trackballs
@eliasr xmoto, hedgewars