Sonic Robo Blast 2 (or SRB2 for short) is a fan made, free Sonic-themed game using a modified version of the Doom engine, based on Doom Legacy (in active development since 1998). The game focuses on recreating the feel of the classic games, as opposed to the newer Sonic that Sega has been making games for now. So far, the current release version is version 2.1.14. It is not yet complete, as some acts of zones are missing, and Dark City is only at the conceptual stage.
As well as the classics, the goal is to go through platforms, defeat enemies and escape from dangers to reach the finish line. In the third act, we face Eggman. In addition to the single player, the game has the following modes for multiplayer: coop, race, competition, match, team match, tag, hide and seek and capture the flag (CTF). More Info »
The game is open source, and anyone can add, modify and customize any part of the game, being able to submit your work in the forums for everyone to play. It also has a wiki for information and the master server to display the multiplayer servers available. Optionally, you can make a game in LAN to play with friends or play in splitscreen on the same computer.