- O & X for Watch
- O & X: Noughts and Crosses
- O is for Obliteration
- O X Master
- O X Multi
- O-ZONE - Protect the Earth
- Oak Island Treasure Hunt
- Occidental Heroes
- Occupy the tribe
- Ocean Wars
- OctoHits
- Octopus Evolution
- Odd Color - Test Your Color Vision
- Odds Are for Messages
- Ode To Heroes
- OEGames Land Navigation
- Off-Road Transport Trailer
- Office Story
- Office Thief - Escape Puzzle
- Officer's Skat
- OffRoad Runway Construction 18
- OG Switch
- OGS Notify
- Oh! Edo Towns
- OH~! My Office - Boss Sim Game
- Oil Barron
- Oil Tycoon 2: Idle Empire Game
- Oil Tycoon: Idle Miner Factory
- Oil Tycoon: Idle Empire Games
- Oil, Inc. - Idle Clicker
- Okey Arataş
- Okhlos: Sigma
- Old-School Snafu
- Olimpo vs Slimes
- Olympus Defense TD. Fury Rome Gods Rising In Divine Dawn Strategy
- Olympus Rising: Hero Defense
- Omar Sharif Bridge Card Game
- Omi Sri Lankan Card Game
- One Block Sudoku
- One Line - Draw Master Puzzle
- One Line Drawing - Duel
- One Night at Flumpty's
- One Night at Flumpty's 2
- One Night at Flumpty's 3
- One Path - Draw Connect Dots
- One Plate!
- One Touch Line Draw Game
- OneBit Adventure
- Onet Classic - Connect Mahjong
- Onet Connect 2016
- Onet Connect Animal Legend
- Online Checkers LiveGames
- Draughts With Friends
- Online Chess LiveGames
- Online Preference LiveGames
- Online Zoo Builder
- Only Flaps And Horses
- Onmyoji
- Onmyoji Arena
- Opacha-mda
- Opdoku = Calcudoku + Mathdoku
- All Lit
- Operation: ATAK
- Operation: ANKA
- Operation Ares - A Revolution on Mars! Recruit Spies, Complete Missions, & Gain Independence
- Operation Optics
- Operation: New Earth
- Optical Inquisitor 17+
- OptiFlight
- Orbeez – O resgate dos Woozers
- Orbit defenders
- Orbit Shots