You can get the following games for free from Stem
Free Games for All Steam Users
- America’s Army 3
- BattleForge
- Between
- Codename Gordon
- COIL
- Mightier
- Peggle Extreme
- Sam & Max: Episode 4
- TrackMania Nations Forever
Free Steam MOD Games for Owners of Any Source (HL2) Engine Game with Source SDK
- Age of Chivalry
- D.I.P.R.I.P. Warm Up
- Darkest Hour
- Dystopia
- Eternal Silence
- INSURGENCY
- Mare Nostrum
- Smashball
- Synergy
- Zombie Panic! Source
If you are an AMD ATI (Radeon) user
- Half-Life 2: Deathmatch
- Half-Life 2: Lost Coast
If you are an NVIDIA user
- Half Life 2 – Death Match
- Half life 2 – Lost Coast
- Peggle Extreme
Read more and get the download link from here