Open Source POS System?

Is anybody running an open source POS system? Our current POS system is very.. well... it's bad. And if we upgrade we'd like to go the open source route as we might be porting from Windows down the road. If I could find a solid product that is Windows and Ubuntu based, that would be great, so I can try it now and implement it later if it works. But worst case scenario, a Linux-only variant may work fine too.

Anybody running one?

We were looking at putting OpenBravo POS into the kitchen at work, but we have started looking at commercial cashless catering offerings now, but were getting on ok with OpenBravo :)

Have a look at this.

I have used this in the past when I was using Windows 98. It has come on loads since then.