Spelunky

Also available on: Mac

Spelunky (now known as Spelunky Classic) was a freeware 2D platform/roguelike game created by independent developer Derek Yu. Later Yu, in cooperation with other developers, made the enhanced remake of the game, it was released on PC and consoles as a commercial game called Spelunky HD, it includes many new areas, enemies, music tracks and 11 new playable characters, plus local multiplayer with co-op mode for 4 players or deatmatch mode.

It is available for purchase on GOG or Steam. The original Spelunky Classic and its source code is available for free on official website

How to Play

Windows

Notes:

Since the game's source code was released for free and available for everyone, fans made unofficial ports to other platforms. The most popular is Spelunky Classic HD, the modified version of Spelunky Classic that adds support for different aspect ratios (originally 4:3 only), touch input, better gamepads support and proper in-game menu. Spelunky Classic HD is available in variants for Windows, Mac, Linux and Android systems, you can find the files on Itch.io page. If you plan to play a Linux port, we also recommend to check this and this pages
Programmer Daniel Zalega also made homebrew ports for PSP and Nintendo DS systems. The game is also can be played in the browser, thanks to HTML5 port
There's also a lot of mods for the game, to find them check Spelunky.FYI website or NexusMods, here's also an article about most popular mods
You can play the game in coop mode with Spelunky SD mod by YellowAfterlife, it fixes several bugs and, most notably, adds online multiplayer support for up to 4 players. Versions for Windows and Linux systems can be downloaded from modmaker's Itch.io page