MegaMek

MegaMek is a "An unofficial, online version of the Battletech board game" which means that you control a set number of huge battle robots against another group. The game takes place on a hex-based map with elevations and movement difficulties. Firing of weapons accumulates heat which may even lead to your mech explode. The game itself is rather complex and nothing for a short leasure but the pro will definitively enjoy this game, or should I say simulation? The game runs out of the box - just better don't use spaces in folder name.

Screenshot by MegaMek Project, displayed here under fair use.