41. Tremulous
This award-winning game combines first-person shooter action with elements typically found in a real-time strategy game. Play as either the aliens or the humans, and rack up wins to become more powerful. Operating System: Windows, Linux, OS X, XBox.
42. Warsow
No, that isn't a misspelling of "Warsaw." Warsow is a very fast-paced, cartoonish shooter featuring rocketlauncher-wielding pigs. Unlike most other shooters, Warsow goes easy on the gore, using stars and cubes to stand in for blood and guts. Operating System: Windows, Linux, OS X.
43. GnomeGames
Gnome's collection of casual "five-minute" games includes Chess, Sudoku, Mines, Four-in-a-row and 11 other simple games. The graphics and gameplay are basic but sometimes addictive. Operating System: Linux.
44. KDE Games
The KDE desktop offers a much wider selection of casual games. It includes KBattleship, KMahjong, KBreakout, KSpaceduel, KMines, KSudoku and many more. Operating System: Windows, Linux.
45. Frets on Fire
The open source answer to Guitar Hero, Frets on Fire challenges you to play along to your favorite songs using a guitar controller or your keyboard. It supports Guitar Hero songs, or you can import songs submitted by other users or create your own. Operating System: Windows, Linux, OS X.
46. StepMania
Very similar to Dance Dance Revolution, Step Mania tests your ability to keep the beat using dance pads or your keyboard. Songs must be downloaded separately from the game, but the site includes hundreds of free songs. Operating System: Windows, Linux/Unix, OS X, XBox.
47. Ultrastar Deluxe
This karaoke games awards points based on how well you sing, similar to the game SingStar. You can use it with your own music files or you can download more than 10,000 songs available for the app. Operating System: Windows, Linux, OS X.
48. GLtron
As in the movie Tron, competitors in this game ride speeding lightcycles that trail walls behind them. The goal is to trap other players, forcing them to hit the wall, while you remain free. Operating System: Windows, Linux, OS X.
49. Ultimate Stunts
A remake of the DOS game Stunts, Ultimate Stunts takes racing to the next level by adding loops, corkscrews, jumps and more. It also makes it easy to build your own tracks. Note that it's still in the earlier stages of development. Operating System: Windows, Linux, OS X.
50. SuperTuxKart
Tux the Linux penguin races around 3D tracks in this racing game. The latest version adds three new tracks, a battle arena, two new weapons and more. Operating System: Windows, Linux, OS X.
51. TORCS
The Open Race Car Simulator (TORCS) offers realistic racing action that figures in tire and wheel properties, aerodynamics, collisions and more. It includes more than 50 cars, 20 tracks and 50 opponents. Operating System: Windows, Linux, OS X.
52. Tux Racer
Downloaded millions of times, this popular classic Linux game features Tux the penguin sliding downhill. It features 3D landscapes and changing weather conditions with fog, high winds and more. Operating System: Windows, Linux, OS X.
The classic Tux Racer (above) hasn't been updated in a while, but this version updates the original with better graphics and gameplay. Operating System: Windows, Linux, OS X.
54. VDrift
This racing game was made with drift racing in mind. It features real-world tracks and vehicles and superb graphics. Operating System: Windows, Linux, OS X.
55. Crossfire
Explore 3000 maps and battle 150 monsters in this retro arcade adventure game. It includes 15 character types, an elaborate magic system and many, many treasures to find. Operating System: Windows, Linux, OS X.
56. Egoboo
This 3D dungeon-crawler challenges players to save Lord Bishop from the clutches of the evil Dracolich, slaying hordes of monsters along the way. Play with up to four other people as you make your way through 40 different dungeons. Operating System: Windows, Linux, OS X.
57. Excalibur: Morganna's Revenge
In this epic adventure game, you begin as a futuristic soldier on a starship but soon time-travel back to the age of King Arthur, where you must save the world from Morganna. It offers 42 levels of solo play and 27 levels you can play with your friends in network mode. Operating System: Windows, Linux, OS X.
If you miss some of the really old dungeon crawlers like Rogue, Hack and Moria, this game is for you. The goal is to retrieve the Orb of Zot from deep in a subterranean cavern and return it to the surface. Operating System: Windows, Linux, OS X.
59. PlaneShift
This 3D fantasy role-playing game offers free play with no restrictions. It features six races, six "Ways of Magic," large worlds to explore and plenty of monsters to fight. Operating System: Windows, Linux, OS X.
60. Ryzom
Set 2000 years in the future on the plant Atys, Ryzom depicts a struggle for world domination between the nature forces of Kami and the technological forces of Karavan. Ryzom is a massively multiplayer online role-playing game (MMORPG) where players move up by gaining experience in fighting, magic, crafting and foraging. Note that while the download and basic play are free, unlimited play requires a subscription. Operating System: Windows, Linux, OS X.