StarCraft 2 has a coop mode which is a ton of fun imo, around 18 different commanders which range from “small spin on an existing race” to “essentially 5 hero characters and no units”. You play with a friend or queue up with a random other player and play from a pool of amped up campaign missions.
No other game comes to mind, but Stormgate also promises a 3vAI mode, which will be playable next week on Steam Next Fest.
New RTS from Warcraft and StarCraft veterans smashes through nearly every stretch goal in $2m Kickstarter campaign, even though it was already fully funded (www.gamesradar.com)