Dunno if anyone's posted this yet, but here's a ton of prototypes for Xbox and Xbox 360 if anyone wants to poke around these.
http://alphaarchive.net/
Edit: to note -- this includes stuff like
for xbox 360:
- Justice League Arcade (canned)
- Project Milo (canned)
- Ace Combat Assault Horizon (according to notes, has a debug menu)
- Crimson Dragon (for xbox 360, which never got ported)
- five builds of CoD4
- eight consecutively dated builds of Stick of Truth
- Alan Wake - Night Springs (original name for American Nightmare)
- "BCG XBLA Test"
for xbox:
- three builds of Ghost Rider (canceled port)
- Fuel (canned game)
- ATV3: Lawless (canned game)
- "Project Velocity (Octane)" (canned game)
- Smash Out (canned game)
- The Red Star (canned game)
- World's Scariest Police Chases 2 (canned game)
and, yknow, more
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