id Software's back catalogue of games will be made available through Valve's Steam digital distribution system after the QuakeCon conference.
That's 24 titles from Commander Keen right up to DOOM 3: Resurrection of Evil, and they'll all work on modern operating systems.
id's also offering an "id Superpack" containing all of them.
- Commander Keen, Episodes 1 through 5
- Wolfenstein 3D
- Spear of Destiny
- Return to Castle Wolfenstein
- Ultimate DOOM
- DOOM II
- Master Levels for DOOM II
- Final DOOM
- DOOM 3
- DOOM 3: Resurrection of Evil
- QUAKE Mission Pack 1: Scourge of Armagon
- QUAKE Mission Pack 2: Dissolution of Eternity
- QUAKE II
- QUAKE II Mission Pack: The Reckoning
- QUAKE II Mission Pack: Ground Zero
- QUAKE III Arena
- QUAKE III: Team Arena
- Heretic: Shadow of the Serpent Riders
- HeXen: Deathkings of the Dark Citadel
- HeXen II
You can see just how much they all cost here.