Games on this list were included based on recommendations, if you'd like to a game added to this list, please post it on the sticky of /f/Games. For a more comprehensive list, please see this Wikipedia page.
- Beneath a Steel Sky - Classic adventure game with excellent artwork and voice talent. Should be available in the Ubuntu repos
- Egoboo - Action-adventure rogue-lite game
- Eldevin - F2P Runescape clone with a distinct charm
- Flare - A surprisingly in-depth and polished isometric RPG
- Lugaru - Turner, is an anthropomorphic rebel bunny rabbit with impressive combat skills. In his quest to find those responsible for slaughtering his village.
- Myst Online: Uru Live - MMO adventure game in where players interact with others to solve puzzles and advance the story.
- ScummVM's Freeware Games - Some fantastic point'n'click games here, my favourite probably being Dreamweb
- Solarus Games - Solarus is a game engine for making Zelda-like games, but there are many completed games available on their website, and also community made games
- Altitude - 2D Online plane combat
- Chromium-BSU - Top-down arcade Shmup
- Kobo Deluxe - 8-way scrolling shooter
- LBreakoutHD - Open-source breakout clones.
- OpenTyrian - The famous Shmup
- SSVOpenHexagon - Open-source clone of Super Hexagon. Source code for packagers
- TeeWorlds - Online 2D shooter
- Witch Blast - Open-source clone of Binding of Isaac. Source code here for packgers.
- OpenTTD - open-source clone of Transport Tycoon Deluxe
- Scorched 3D - Simple turn-based or real-time artillery strategy game
- Simutrans - Open-source transportation simulator clone.
- Unknown Horizons - Village builder inspired by the Anno series
- Widelands - Polished Settlers clone
First Person Shooter
- Alien Arena - Retro Sci-Fi Online FPS
- ET Legacy - Wolfenstein: Enemey Territory for modern systems
- Cube 2 - Quake-like Arena online FPS with multiple game modes
- Freedoom - The Freedoom project aims to create a complete free content game based on the Doom engine.
- OpenArena - Online arena FPS using the id tech engine
- OpenSpades - Clone of Ace of Spades 0.75, featuring fully destructible terrain and plenty of game modes (including the well-known Capture the Flag).
- Red Eclipse (GNU/Linux, BSD, Windows & Mac) - a free online arena shooter with parkour.
- Termulous - RTS/FPS Hybrid with aliens!
- The Dark Mod - Fan-made spin-off the the fantastic Thief series (Not suitable for low-end systems)
- Urban Terror - Fast paced online FPS reminiscent of Counter-Strike
- Warsow (GNU/Linux, Windows & Mac) - a fast-paced FPS in a futuristic cartoonish world.
- Xonotic (GNU/Linux, BSD, Windows & Mac) - a free online shooter, based on Quake.
- Ryzom A game where there are no classes to choose, nor force to choose a faction or guild.
- Manic Digger
- Minetest - (GNU/Linux, FreeBSD, Windows, Mac & Android) - Uses C++, Requires mods to be fun
- Terasology - Fancy lookin' Minecraft
- TrueCraft - Clean-room implementation of Minecraft 1.7.3
- Voxelands - standard clone?
- voxel.js - Tool for creating minecraft clones
- 2048 (Browser) - a sliding addition game.
- Blockout2 - 3D Tetris
- Duck Marines - Open-source clone of Chu Chu Rocket. Source code here for distro packagers.
- FloboPuyo - Open-source clone of PuyoPuyo. Source-code for packagers
- Frozen Bubble - Open-source clone of Bubble Bobble.
- Not Tetris 2 - Tetris with physics
- Pingus - Lemmings clone.
- Portable Puzzle Collection - 39 old school puzzle games
- Speed Dreams - Realistic racing sim
- SuperTuxCart - Open-source clone of the Mario Cart games (Not suitable for low-end systems)
- Yorg - A top-down racer in the Micro Machine's style.
- Roguebox Adventures - Neat little graphical rogue-like with a focus on survival and crafting. Source code here for packagers
- Cataclysm: Dark Days Ahead - Unique zombie survival rogue-like, very thrilling to play.
- UnReal World - Crazy in-depth survival roguelike based in iron age Finland
- Dungeon Crawl Stone Soup - A roguelike adventure to find the mystifyingly fabulous Orb of Zot.
- NetHack - Does this need an introduction?
- Brogue - Your goal is to travel to the 26th subterranean floor of the dungeon, retrieve the Amulet of Yendor and return with it to the surface.
- Tales of Maj'Eyal: Age of Ascendancy - Ultra polished graphical roguelike with the option to save your game
- ADOM (Ancient Domains of Mystery) - Another great roguelike, with a huge world and many ways to play
- DoomRL - DOOM, but roguelike!
- Angband (GNU/Linux, Windows, Mac & Android) - a single-player dungeon exploration game in the universe of JRR Tolkien.
- Shattered Pixel Dungeon (Android) - a traditional roguelike game with pixel-art graphics and simple interface.
- Cataclysm DDA - Cataclysm: Dark Days Ahead is a turn-based survival game set in a post-apocalyptic world
- Star Ruler 2 - Explore, expand, exploit and exterminate your way to become the ruler of the Galaxy.
- Mr. Rescue - Play as a fireman rescuing people. Source code here for people who want to package it for their distro
- Sienna - Fun little runner/platformer. Source code
- Super Tux - Open-source Mario clone, and currently in need of help if it's to stay alive
- Secret Maryo - Mario 3 Clone
- Hurrican - Inspired by the classic game Turrican. Mostly forgotten nowadays, so you may have to compile it from here
- Frogatto - Platformer with great music and graphics. Should be available in the Ubuntu repos for free
- Commander Keen 4 - Classic Shareware DOS title ported to Linux
- OpenClonk - Weird Online 2D Mining
- Mari0 - Odd mix of Mario and Portal.
- OpenTTD (GNU/Linux, Windows & Mac) - a transport simulation game based upon the popular game Transport Tycoon Deluxe, written by Chris Sawyer.
- OpenRCT2 (GNU/Linux, Windows & Mac) - An open source reverse engineering of Rollercoaster Tycoon 2. Requires assets from the original game, acquirable here
- Ur-Quan Masters - Updated version of Star Control II. Be sure to download the Voice Pack! (Alternative HD version available here)
- Endless Sky - 2D space trading and combat game similar to the classic Escape Velocity series
- Oolite - Well done Elite remake, with plentiful mod support.
- Pioneer - a remake of the sequel to Elite, Frontier.
- Vega Strike - Open Source 3D Action-Space-Sim
- Naev - open-source game about space exploration, trade and combat
- 0 A.D. (GNU/Linux, Windows, Mac) - a game of ancient warfare.
- The Battle For Wesnoth (GNU/Linux, Windows, Mac, Android & iOS) - a turn-based strategy game with a high fantasy theme.
- Freeciv (GNU/Linux, Windows) - A clone of Civilization II from the Sid Meier's Civilization series.
- Widelands (GNU/Linux, BSD, Windows & Mac) - A real-time strategy game focused on building an economy. Based on Settlers 2.
- FreeCol - Clone of Colonization
- FreeOrion - Clone of Master of Orion
- OpenRA - Open-Source implementation of C&C: Red Alert, Tiberian Sun, and Dune 2000
- Tanks of Freedom - Turn based strategy, similar to Advance Wars on the GBA.
- Hedgewars - Clone of the game Worms
- UFO: Alien Invasion - Turn-based tactical combat game, inspired by the X-Com series.
- Argentum Age - Open-source fantasy card game
- UFO2000 - Another X-Com inspired game
- Wyrmsun - An interesting fantasy RTS
- Spring RTS - RTS game engine that has a few complete games made from it, like Zero-K
- Warzone 2100 - 3D RTS that offers campaign, multi-player, and single-player skirmish modes.
- Megaglest - RTS where you control the armies of one of seven different factions
- PokerTH - Free online poker with the best open source texas holden poker game and a great community
- Seven Kingdoms: Ancient Adversaries - GPL release of Seven Kingdoms: Ancient Adversaries