A brief and incomplete list of reverse-engineered and original vintage-gaming sourcecode for systems based on my favourite CPU, the 6502.
Crazee Rider (1987) - Original sourcecode.
Galaforce 1 (1986) - Original sourcecode.
Planetoid (1983) - Disassembly.
Planetoid (1983) - Disassembly.
Bilestoad, The (1982) - Original sourcecode.
Bomber (1978) - Commented disassembly.
Deathmaze 5000 (1980) - Commented disassembly.
Elite (1985) - Partially commented disassembly.
Epoch (1981) - Commented disassembly.
Phantom's Five (1980) - Commented disassembly.
Pinball Construction Set (1982) - Original sourcecoce.
Prince of Persia (1989) - Original sourcecode.
Robotron 2084 (1983) - Commented disassembly.
Scott Adams Adventures (1981) - Commented disassembly.
Space Eggs (1981) - Commented disassembly.
Stellar 7 (1983) - Commented disassembly.
Asteroids (1979) - Original sourcecode.
Asteroids (1979) - Fully commented disassembly.
MULTIPLE - Many Atari games disassembled in this repo!
A-Team (19xx) - Partially commented disassembly.
Air Sea Battle (1977) - Fully commented disassembly.
Berzerk (1982) - Fully commented disassembly.
Combat (1977) - Fully commented disassembly.
Cosmic Ark (1982) - Fully commented disassembly.
Donkey Kong (1982) - Fully commented disassembly.
Dragonfire (1982) - Commented disassembly.
Dragster (1980) - Commented disassembly.
Freeway (1981) - Fully commented disassembly.
Haunted House (1982) - Partially commented disassembly (WIP).
Indy 500 (1977) - Partially commented disassembly.
Jawbreaker (1982) - Fully commented disassembly.
Kaboom (1981) - Fully commented disassembly.
Outlaw (1978)- Fully commented disassembly.
Pitfall! (1982) - Commented disassembly.
Pitfall! (1982) - Fully commented disassembly.
Red vs. Blue (1981) - Fully commented disassembly.
Riddle of the Sphinx / Dank Tower (1982) - Fully commented disassembly.
River Raid (1982) - Fully commented disassembly.
Space Jockey (1982) - Fully commented disassembly.
Star Master (1982) - Fully commented disassembly.
Surround (1977) - Fully commented disassembly.
Venture (1981) - Fully commented disassembly.
Asteroids (1987) - Original sourcecode.
Centipede (1987) - Original sourcecode.
Commando (1989) - Original sourcecode.
Crossbow (1988) - Original sourcecode.
Dig Dug (1987) - Original sourcecode.
Food Fight (1987) - Original sourcecode.
Galaga (1986) - Original sourcecode.
Hat-Trick (1987) - Original sourcecode.
Joust (1988) - Original sourcecode.
Ms. PacMan (1986) - Original sourcecode.
Robotron 2084) (1987) - Commented disassembly.
Robotron: 2084 (1987) - Original sourcecode.
Sphinx - Original sourcecode.
Super Stunt Cycle (1989) - Original sourcecode.
Xevious (1986) - Original sourcecode.
Anteater (1982) - Original sourcecode.
Blue Max (1983) - Original source code in this thread.
Bruce Lee (1984) - Commented disassembly.
Buck Rogers: Planet of Zoom - Original source code listing from paper.
Dandy (1983) - Original sourcecode.
Donkey Kong (1983) - Original sourcecode.
Fort Apocalypse (1982) - Original sourcecode.
Getaway! (1982) - Original sourcecode.
M.U.L.E. (1983) - Commented disassembly. + Comprehensive document
PAC-MAN (1982) - Original sourcecode.
Pinball Construction Set (1983) - Original sourcecode.
Preppie! (1982) - Original sourcecode.
Preppie! II (1983) - Original sourcecode.
Princess and the Frog, The (1982) - Original sourcecode.
Sea Chase (1983) - Original sourcecode.
Sea Dragon (1982) - Original sourcecode.
Star Raiders (1979) - Fully commented disassembly.
Star Raiders (1979) - Original source code listing from paper.
Up'n Down (1983) - Original source code listing from paper.
Aviator (1983) - WIP.
Crazee Rider (1987) - Original sourcecode.
Exile (1988) - Fully commented disassembly.
Elite (1984) - Original sourcecode.
Galaforce (1986) - Original sourcecode.
Manic Miner (1984) - Fully commented disassembly.
Revs (1985, 1986) - Fully commented disassembly.
Stunt Car Racer (2019) - 6502. BBC Micro port of Stunt Car Racer.
Thrust (1986) - Fully commented disassembly.
Alien 3 (1992) - Original sourcecode.
Altered Beast (1989) - Original sourcecode.
Atomic Robokid (1990) - Original sourcecode.
Attack of the Mutant Camels (1983) - Fully commented disassembly.
Beach Head (1983) - Fully commented disassembly.
Bounty Bob Strikes Back (1984) - Fully commented disassembly.
Castles of Dr. Creep III (1984) - Fully commented disassembly.
Commando (1985) - Fully commented disassembly.
Elite (1985) - Commented disassembly and patches.
Habitat (1986) - Original sourcecode.
Hunchback (1984) - Fully commented disassembly.
Gridrunner (1983) - Fully commented disassembly.
Kickman (1982) - Original sourcecode.
Laser Zone (1983) - Commented disassembly. WIP.
Le Mans (1983) - Fully commented disassembly.
Lode Runner (1983) - Fully commented disassembly.
Miner 2049'er (1983) - Fully commented disassembly.
Nemesis the Warlock (1987) - Original sourcecode.
Omega Race (Ultimax) (1982) - Original sourcecode.
Rampage (1987) - Original sourcecode.
Slaine (1987) - Original sourcecode.
Skool Daze (1984) - Commented disassembly.
Stunt Car Racer (1989) - Partially commented disassembly, from the BBC port project.
Wizard of Wor (Ultimax) (1982) - Original sourcecode.
Wizard of Wor (Commodore) (1983) - Commented disassembly.
Akira (1988) - Partially commented disassembly.
Backgammon (1990) - Partially commented disassembly.
Balloon Fight (1984) - Commented disassembly.
Chip'n'Dale 2 (1992) - Partially commented disassembly.
Contra (1987) - Fully commented disassembly.
Days of Thunder - Unreleased (1990) - Original sourcecode. Game was never released.
Dragon Warrior (1987) - Fully commented disassembly.
Final Fantasy (1987) - Fully commented disassembly.
Green Beret (1987) - Partially commented disassembly.
HeroQuest (Unreleased) - Original sourcecode.
Jackdal (1988) - Fully commented disassembly.
James Bond Jr. (1991) - Original sourcecode.
Magician (1990) - Original sourcecode.
Mega Man 3 (1990) - Partially commented disassembly.
Mega Man 4 (1991) - Partially commented disassembly.
Mega Man 5 (1992) - Partially commented disassembly.
Mega Man 6 (1993) - Partially commented disassembly.
Metroid (1986) - Fully commented disassembly.
Mike Tyson's Punch Out! (1987) - Partially commented disassembly.
New Ghostbusters II (1992) - Partially commented disassembly.
Ninja Hattori Kun (1986) - Original sourcecode.
Robocop 3 (1992) - Partially commented disassembly.
Sim City (Unreleased, 1991) - Partially commented disassembly.
Super Mario Bros (1985) - Fully commented disassembly.
Super Mario Bros 3 (1990) - Commented disassembly.
Tetris (1989) - Commented disassembly.
Zelda, The Legend Of (1985) - WIP, partially commented disassembly.
Zelda, The Legend Of (1985) - Fully commented disassembly.
http://bringerp.free.fr/RE/index.php5 - MULE and others.
https://github.com/milkeybabes - C64 original sources.
https://github.com/billbudge - Author of Pinball Construction Set.
http://www.qotile.net/minidig/index.html - Several Atari 2600 disassembly sources.