MegaMek is developed and maintained by a community of volunteer programmers, with a small core of developers supported by numerous contributors. The project is hosted by SourceForge.net and is distributed with its source under the GNU General Public License. The game is written entirely in Java with graphics based on Swing (an AWT interface also exists, but it's not updated with the newest features), resulting in reasonable playability even on low-end platforms.
Currently, MegaMek supports all the rules from the BattleTech introductory box set, most of the rules from the Total Warfare core rulebook, and a number of advanced rules from the Tactical Operations rulebook and some house rules. The game offers a simple genetic-algorithm-driven bot that one can play against, though so far its intelligence is limited. Also, most of the AeroTech rules from Total Warfare are implemented. An optional 3D interface is currently under development. The game currently supports multiplayer via TCP/IP, though play-by-email is possible through the exchange of saved games.
A sister project MekWars that is also written in Java gives MegaMek a campaign structure with a chat interface, hangars, accounts, repairs, and numerous other settings which can be defined by each server administrator as she or he wishes. There are numerous MekWars servers which offer campaigns in the different eras of BattleTech.