Mechcommander Online is a registered trademark for the Mechcommander community who play multiplayer over at gameranger, it's all about multiplayer action for Mechcommander Fans!
MechCommander however, is a real-time tactics (RTT) video game based on FASA's BattleTech/MechWarrior franchise (though often being called a real-time strategy game), developed by FASA Interactive and distributed by MicroProse. MechCommander was released in 1998.
It had an expansion which was later combined with the original title and released as MechCommander Gold.
A sequel also exists (distributed by Microsoft)MechCommander 2.
MicroProse also used many of the ideas in their 2000 Starship Troopers game.
MechCommander, in being a squad-based RTT, is more in the lines of X-COM:
Apocalypse than RTS games like Age of Empires or StarCraft.