Similar to ファイナルエクセリオン

The Awesome Adventures of Captain Spirit

Orbiter (simulator)

OpenTTD

Osu!

Otometeki Koi Kakumei Love Revo!!

Oni (video game)

Off (video game)

Operation Flashpoint: Cold War Crisis

Operation Flashpoint: Dragon Rising

Half-Life: Opposing Force

Omoide ni Kawaru Kimi: Memories Off

Ori and the Blind Forest

We Without Wings