Downloading MegaMek 0.4 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. This free Mac app is an intellectual property of Nicholas Walczak. The default filename for the application's installer is megamek-0.38.0.tar.gz. We recommend checking the downloaded files with any free antivirus. The most popular version of the tool is 0.3.
From the developer:
MegaMek is an unofficial, online version of the Classic BattleTech board game. It includes many of the optional rules and technology from Tactical Operations, including advanced terrain and planetary conditions. You can choose ground, atmosphere, or space combat, using Total Warfare rules.