Fusion Ticket is an opensource box office and ticket sales website.
It is designed for you to set up a venue and event choose your type of payment and then let users buy tickets.
It is all fully automated, it includes such things as:
Custom Seating plan
Paypal Intergration Using IPN
Ticket and email customisable templates
Box office frount end for more fexible useage
Smarty template system
And much more!