My client is a very small non-profit museum in need of a simple way to collect admission fees from visitors and handle a small number of retail sales. They have approximately 100 transactions per day and need to be able to process credit cards. Some built-in reporting would be nice too, but if it's mySQL-based we can manage that outside the product if need be.
I was thinking of a web-based app, so does the hardware matter? Client does not need a cash register. The website is hosted by a shared-hosting provider that offers cPanel and Fantastico. The hosting package also includes unlimited sub-domains and mySQL databases.
I don't know of a web application that would fit your needs, but there are plenty of free POS programs for the PC. Integrating the credit cards in would be harder, I dont know if the free ones would support that.