Title: MegaMek
Developer: Ben Mazur and others
Date Published: ?
Platforms: Java
MegaMek is a very promising turn-based strategy game, written in Java and distributed under GPL.
MegaMek uses BattleTech rules, and has most of the BattleMech and weapon details right.
It gets better all the time. These days it fully supports the Level 1 rules and technology (Inner Sphere technology from year 3025 only), and it is getting better and better support for Level 2 and Level 3 rules (OmniMechs and Clan versions of the weapons are there already, so we can bash 'round with all the nice Clan stuff). Hopefully it'll get even farther and farther with this, but it's already good enough for casual metal-twisting.
Most of the work so far has been put to the rules, so there are still technical things; There's only a TCP/IP multiplayer game available (you can, of course, play multiplayer game on same computer by running multiple game clients, with one acting as the server), but there already is a primitive "bot" to play with if you want to play single-player matches (though the bot is still pretty limited). The graphics are somewhat lacking (Icons are rather plain, but some mechs already have graphics of their own in v0.28!). There's no sound effects or other unnecessary "multimedia stuff". Also, the game displays information all the way down to the Battletech tabletop detail, and weapon fire is shown only as lines, so this may be a dry experience for most computer game players, but we tabletop players don't care =) Still, it's not as dry as I'd imagine; The graphics don't exactly eat my eyes, and are nicely enough done.
If you're interested of BattleTech not from the simulation side but rather as a strategy game, I can definitely recommend this, because there quite likely is no other equally up-to-date turn based strategy games on this topic. This game is so hard-core you can smell the almighty distance-calculating rubber bands. However, if you want simulation stuff, you still need to get commercial games like the Mechwarrior series (I still pretty much recommend Mechwarrior 2...)
Home page: http://megamek.sourceforge.net/