Lemon is an opensource point of sale for linux, and other unix. 
It is a general pos, not targetet to a specific business.

It has been developed for ease of use and customization, and to support
barcode scanners and ticket printers. At this point, it has been tested
with a parallel port ticket printer (Star Micronics, SP500).

More information on http://lemonpos.sourceforge.net/
