I don't like the idea of having a large system. I like components I can swap in and out so if I am lacking a feature, I can use something else rather then live with it or start cover with a different system. It looks like there are systems that do it all.
I need something to allow customers to buy something. Kickstart a script I have. Register the user in a ticketing system for customer support. Notify me when their support has expired (also tickets should only be available to customers).
A bonus would be if I can have forum software and a mailing list. Is there a good combination of software that I can use?