Odyssey: The search For Ulysses  

Of Light and Darkness

Opera Fatal

Operation Flashpoint

Original War

Orion Burger

Orion Conspiracy 

Orlando Jack

Other Worlds (free game)

Out of Order (free game)

Outcast 

Outcry/Sublustrum

Overclocked: A Story About Violence

Overseer Tex Murphy

Oz orwell and the crawling chaos (Video WT)

Ozzie and the Quantum Playwright (free game)