One of the very greatest, and for some reason, least-known, libre games is The Dark Mod, a recreation of the Thief series for modern PCs.
I had eagerly installed the game from the AUR, but was dismayed to have no missions installed. There was no access to download missions.
However, today, thedarkmod-bin was updated on my system, along with all the missions!
For anyone who likes stealth games, this is the OG stealth game, made modern!
[EDIT] I apparently spoke too soon. The game loads, but no assets are found. Still no response from servers.