Revel Systems API makes it possible to run a cash register, a restaurant and a mobile point-of-sale system with an iPad as the center of the User Interface. Check out what Revel has to say about the API on their website.
The grocery store set up supports self-checkout and has a number of payment plug ins including Dwolla and Levelup.
As Techcrunch reported in early October, "Revel has been on a roll, raising a $3.7 million Series A in May of 2011 and apparently hitting their stride in terms of revenue generation on the back of that relatively small amount, impressive for a company whose product involves quite a few hardware components. There’s also its partnership with Best Buy’s Geek Squad, which provides a service and installation arm for its customers, while avoiding the costs of maintaining that kind of force on staff at all times. Falzone said that’s what’s next for the company is a big hiring push, to grow the 30-person team, particularly by adding new experienced sales staff and additional engineers."
As Gigaom's Erica Ogg suggested, Revel "needs to get a national chain to buy into its system, but that’s obviously easier said than done."
Finally, Darrell Etherington of Betakit reports that Revel Systems' next big target is the hotel market.