Allegro is a multi-platform game library for C/C++ developers that provides many functions for graphics, sounds, player input (keyboard, mouse, and joystick), and timers. It also provides fixed and floating point mathematical functions, 3D functions, file management functions, compressed datafile, and a GUI.
Atanks is a multi-platform Scorched Earth clone similar to the Worms series of games. Annihilate the other tanks to earn money, then spend it on bigger and better shields and weapons to wipe out the opposition. It features a wide array of weapons, AI players, destructible landscape, weather, parachutes, teleports and a wide range of other features.
ZSNES is an SNES emulator for i386 machines running Linux, DOS, or Windows. It allows you to play most SNES games on your PC. It also adds several enhancements not present in the original SNES such as filters to improve image quality, savestates to be able to save/restore your game at any time, and more.
Slash'EM (Super Lotsa Added Stuff Hack -- Extended Magic) is a variant of the hugely popular roguelike game NetHack. It adds more monsters, more objects, more dungeon levels, more roles, and more races, shopkeeper services, and techniques for you to use, and invisible objects and gypsies for those who feel lucky. It also comes with a GTK windowing interface and higher resolution tile sets as options.
gnuboy emulates the Color GameBoy handheld console in portable C, with interfaces for X11, Linux fbcon and svgalib, SDL, DOS, and Windows, with other ports planned in the future. Compatibility with ROMs tested is around 99 percent, and all major hardware features except SGB extensions are supported. With the optional optimized i386 assembly code, gnuboy can run at the full 60 FPS even on Pentium/75s and below. No special libraries are required to compile, and gnuboy is known to build on many *nix variants.
Vavoom is a DOOM source port incorporating Doom, Heretic, Hexen, and a little bit of Quake. It runs on DOS, Windows, and Linux and includes many advanced features like OpenGL and Direct3D support, translucency, freelook, jumping, a client/server architecture with in-game joining, a Quake-style console, a powerful language to describe game logic (Vavoom C), and much more.