On the Road: Truck Simulator
On the Western Front
On-Together: Summer Studies
Oolite
Oops Airlines
Open Bar
OpenBlocks
Open Land
OpenRCT2
OpenTTD
Operation Breadcrumbs
Operation Deep Magic: Cryptanalysis
Operation: Forge the Deep
Opus Magnum: De Re Metallica
Opus: Rocket of Whispers
Orange Season
Orbital
Orbital Gear
Orbiter
Orbit HD
Orbit: Playing with Gravity
Orb of Aeternum
Orb of Creation
Orbosis Gloriosis