Open Source Point of Sale software?

DogDude writes: "I own a brick-and-mortar retail store. We do a good volume of business, and we plan to start opening more locations soon. We've outgrown out current Point-of-Sale system (POS), and I'm shopping for a new one. There are plenty of good, mature, proprietary systems out there already. I'm looking for information on OSS POS systems that are also mature, stable, and well supported. It seems that most OSS POS projects are either tiny, relatively unsupported, and lacking many critical features, or they're so large and complex that they can only be implemented by a Fortune 500 company with a dedicated IT staff. I'm looking for something robust that will work out of the box, yet still scale appropriately for a mid-sized company. Suggestions?"