I'm still not entirely clear on what an "economic RTS" is, but I like the concept of a game that encourages and rewards predatory economic policy on a large scale, especially one being made by the lead designer and AI programmer of Civilization IV. That fellow, Soren Johnson, announced that a prototype his new game, Offworld Trading Company, is now available to play, although there are a couple of catches.
Mohawk Games—the indie studio co-founded by Civilization 4 lead designer Soren Johnson—have officially unveiled their first game. Offworld Trading Company is an economy-based RTS in which money is your greatest weapon. In the metaphorical sense, I'd hope—unless we'll be ordering hundreds of units to stuff pounds, dollars and euros into custom-made muskets, with marginal stat boosts based on the weight and heft of a faction's currency.