What is "megamek"

MegaMek is an open source, turn-based strategy computer game that simulates the Classic BattleTech board game. MegaMek is not licensed by or affiliated with Topps or Catalyst Game Labs, the owners and publishers of the BattleTech line, but is nonetheless a faithful simulation of the game. Exceptions are a few trademarked items changed by the developers (e.g., changing 'Mech to Mek).