Super Mario War is an open-source, cross-platform, platform-adventure video game and level editor released on 16 December 2006. It is based upon gameplay elements and audiovisual media that are cloned from Nintendo's Super Mario series.
Wolfenstein 3D is a first-person shooter video game developed by id Software and published by Apogee Software and FormGen. Originally released on May 5, 1992 for DOS, it was inspired by the 1981 Muse Software video game Castle Wolfenstein, and is the third installment in the Wolfenstein series. In Wolfenstein 3D, the player assumes the role of Allied spy William "B.J." Blazkowicz during World War II as he escapes from the Nazi German prison Castle Wolfenstein and carries out a series of crucial missions against the Nazis. The player traverses each of the game's levels to find an elevator to the next level or kill a final boss, fighting Nazi soldiers, dogs, and other enemies with knives and a variety of guns.
Arena 93 is a retro 3d maze shooter. The game comes from the vaporwave website http://windows93.net.
Pac-Man is a maze arcade game developed and released by Namco in 1980. The original Japanese title of Puck Man was changed to Pac-Man for international releases as a preventative measure against defacement of the arcade machines by changing the P to an F. Outside Japan, the game was published by Midway Games as part of its licensing agreement with Namco America. The player controls Pac-Man, who must eat all the dots inside an enclosed maze while avoiding four colored ghosts. Eating large flashing dots called "Power Pellets" causes the ghosts to turn blue, allowing Pac-Man to eat them for bonus points.
More games can be found here that are all open source games and game-related projects that can be found on GitHub - old school text adventures, educational games, 8-bit platform games, browser-based games, indie games, GameJam projects, add-ons/maps/hacks/plugins for commercial games, libraries, frameworks, engines, you name it.