SmallPOS is a POS and accounting system for small business written using Seaside web application framework for Smalltalk. Pharo is used as platform and the Code is on SqueakSource. The license of SmallPOS is MIT.
SmallPOS itself is a framework that can be used to build POS management applications.
Looks like there are some activity now to update the framework code and there are some screenshots of a russian SmallPOS-based management system that was built with the SmallPOS framework (click to enlarge):