I've always been a Battletech fan and as such am currently attempting (in a solo effort) a Battletech (MechAssault) total conversion, based on the game rules from Aerotech and Battlespace.
It's in the preliminary stages right now, as the changes I'm first focusing on are primarily the cosmetic ones, but I've got a good idea about how I want to modify the tech tree and ship components. The setting will be 3058, and the available nations will be the Capellan Confederation, Draconis Combine, Federated Suns, Free Worlds League, Lyran Commonwealth, Clan Ghost Bear, Clan Jade Falcon, Clan Smoke Jaguar, and Clan Wolf.
I'll post more about it when I've gotten more substantially into it.
I believe there was a prior effort for a Battletech one but I get the impression they were hampered by feature creep (like making custom models for each ship) and scrapped the project. I'm planning on staying far, far away from any custom art.