A lot of unannounced games has been spotted in Steam registry, including PC versions of Halo 3, Halo 2, Second Life, Cut the Rope, Resident Evil: Revelations, Dyad and Fez.
The big surprise is Halo 3 here which was never developed for PC and was an Xbox 360 exclusive. If you think it's a hoax, this is the tool which people use to peek into Steam's database and Halo 3 has been listed as ValveTestApp216800.
The list of unannounced games:
- La-Mulana
- The Splatters
- Octodad: Dadliest Catch Beta
- Duke Nukem 3D: Atomic Edition (Duke Nukem 3D+)
- Super House of Dead Ninjas
- Fez
- LucasArts Test App
- Fast and Furious 6
- Lococycle
- Yogventures!
- Hardware
- Hardware (Demo)
- Dyad
- Cut the Rope
- Shadow Warrior Complete
- Hardware (VIP)
- Hardware (Internal)
- THE KING OF FIGHTERS XIII
- Retro/Grade
- Resident Evil: Revelations
- THE KING OF FIGHTERS 2002 UNLIMITED MATCH
- THE KING OF FIGHTERS ’98 ULTIMATE MATCH
- Quantum Conundrum 2
- Halo 3
- Halo 2
- Halo: Combat Evolved
- The Witness
- Angry Birds Space
- Angry Birds Seasons
- Second Life
Source: NGAF