Section 6
- observer
- ogamesim
- omega-rpg · a hack-style game with quests.
- oneisenough · 2D platform game about communist and capitalist balls
- oneko
- onscripter · NScripter-compatible visual novel games engine
- onscripter-1byte · NScripter-compatible visual novel games engine
- oolite · a space-sim game
- oonsoo · Solitaire card game for x11
- open-invaders · Space Invaders clone
- openarena · OpenArena client
- openarena-server · OpenArena dedicated server
- openbve · train/railway simulator and game
- openbve-objectviewer · Development tool for openBVE
- openbve-routeviewer · Development Tool for openBVE
- opencity · a 3D city simulator game
- openclonk · multiplayer game of strategy, action and skill
- OpenJazz · Jack Jazzrabbit 1 game engine reimplementation
- openlugaru · Third-person rabbit action game
- openmrac · split-screen multiplayer 3D racing game
- openmw · Reimplementation of the Morrowind Engine
- openmw-cs · Construction Set Editor for OpenMW
- openmw-iniimporter · Import the ini variables from Morrowind to OpenMW
- openmw-launcher · Graphical launcher for OpenMW
- openrct2 · open source re-implementation of “RollerCoaster Tycoon 2”.
- openrct2-cli · Headless server mode for OpenRCT2
- openrpg-client · The client for OpenRPG
- openrpg-server-cli · The command line server for OpenRPG
- openrpg-server-gui · The graphical server for OpenRPG
- openssn · modern submarine tactical simulator
- OpenStereogram · autostereogram generator
- openttd · open source clone of the Microprose game “Transport Tycoon Deluxe”
- opentyrian · an open-source port of the DOS game Tyrian
- openyahtzee · play a classic game of Yahtzee
- orbit · space combat simulation
- os_mon
- osmose-emulator · is for Master System and Game Gear consoles with excellent performance and compatibility in emulated games.
- overgod · a bi-directional scrolling arcade game
- overkill · bloody 2D action deathmatch-like game in ascii-art
- overkill-bot · bloody 2D action deathmatch-like game in ascii-art
- overkill-editor · bloody 2D action deathmatch-like game in ascii-art
- overkill-server · bloody 2D action deathmatch-like game in ascii-art
- overkill-test-server · bloody 2D action deathmatch-like game in ascii-art