All Linux POS solution: http://www.netpos.com
Didn't Retailix win Tescos and then dumped the Linux solution when MS dropped their trousers and repriced the licenses ?
PCMS were the first to have a deployed linux solution in the UK running with Beanstore.
On another note, GNU-Solutions in the UK have a Retail Hardened Linux Distribution (Gazelle) and provide services, consultancy and 24x7 support. .
( from the department of shameless plugs...... )
...so does Apropos Retail. They've been shipping Linux POS for years.
Well, have you heard of Retalix.
POS systems is what they do and they have linux solutions.