Similar to ライズ:サン・オブ・ローマ

Orbiter (simulator)

OpenTTD

Osu!

Otometeki Koi Kakumei Love Revo!!

Oninaki

Bail or Jail

Operation Flashpoint: Cold War Crisis

Operation Flashpoint: Dragon Rising

Half-Life: Opposing Force

Omoide ni Kawaru Kimi: Memories Off

We Without Wings