Request Tracker, also known as RT,  by Best Practical is among the best TTS (Trouble Ticket System) of all and also happens to be Open-Source. RT is very flexible and powerful, but is also easy to learn and to customize.

Purchase, Sales, IT or Support – RT can be used almost everywhere. Even if it is just getting order in a large mailbox, RT can handle it!

We use RT for client support, as a lot of the other large companies out there.