Windows (3.1 - 10)

Free Games

78641

0 AD, RTS, similar to Age of Empires

Abashera

Barkley, Shut Up and Jam

Bat Castle

Battle of Wesnoth, turn-based strategy

Battleships Forever, RTS

Bubsy 3D: Bubsy Visits James Turrell Retrospective

Cannonball, open-source OutRun port

Cave Story, you probably know this game.

Classic Game, like ???

Crypt Worlds

Dongland Repainted, I don't even know anymo

Duck Marines, Chu Chu Rocket clone, open-source

Dungeon Crawl Stone Soup, roguelike, 'nuff said >:D

Enviro-Bear 2000, lol

Flight Gear, flight simulator

Freeciv, Civilisation clone, open source

Foreverhood

Four Winds Fantasy DX

Ghosts of Aliens

Gingiva

Hedgewars, Worms clone, open-source

I Wanna Be The Guy, oof

illegal crime game

Irusu Syndrome, Japanese puzzle game, English patch

Jake Clover's games

Kill Dad

Knytt, explore world, find UFO

Lisa the First, I really need to play the Lisa series aaaah

Lost in the Static, " free exploration-oriented platform/jumping game"

M dot Strange's games

magicweedoo's games

Mari0, Super Mario Bros., but with some Portal flavours

Mega Man 8-bit Deathmatch, FPS Mega Man game

Middens

Minetest, Minecraft clone, open-source

Nethack, 'nother roguelike, 'nuff said >:D

Off

Openarena, FPS based on idTech3, open-source

Openra, Command and Conquer clone, open-source

Openttd, Transport Tycoon Deluxe clone, open-source

Painted Tomb, "A story of companionship, betrayal, misguided inclinations toward revenge and ultimately the road to something else (although the pain and memory of misgivings may linger.)"

Photopia, interesting interactive fiction

Pirate Kart V, and pretty much the entirity of Glorious Trainwrecks

Sonic Robo Blast 2, Sonic on Doom engine. Surprisingly awesome

Super Tux Kart, kart racer with the linux mascot

Tiny Fragments, neat puzzle game

thecatamites' games, some of these are not free mind you, but most are. Space Funeral is their most known game, but is highly recommended.

TUMIKI Fighters, pastel shmup

UFO Alien Invasion, XCOM clone, open-source

The Underground Explorer

Vidiot Game

Warning Forever, bossrush shmup

Which, short horror game

The White Chamber, point 'n' click sci-fi horror

Xocotl: God of Stars

Xonotic, FPS similar to Quake and Unreal Tournament, open-source

Yume Nikki, does it need an introduction? It's an amazing experience!

Zero-K, RTS with robots