slightly different scope, but i had a customer that owned a couple restaurants and had a custom POS written in vb.net that they were trying to turn into a product to market to other restaurants. it was very poorly written and their developer eventually bailed on the project, but it had everything from food order entry screens, to food supply inventory, to employee management and interfacing with a badge/swipecard printer, to a map editor for the layout of the restaurant to be able to track which waitresses had which tables.
what have you seen in POS systems that you didn't like that would make you want to create a new one?
http://checkoutapp.com/ looks like a nice system for a mac-based store.
