Thanks to JC-S60, here's a
link to a list of Car PC front ends and support software.
What is a front end? A front end is a unifying application that provides a common interface to several functions in the Car PC. Commonly, those functions are Music (mp3's, and other formats), DVD's, Photos, Telephone control, etc. Many front ends allow you to embed applications such as navigation inside the front end to prevent you from having to switch to that application.
Support software performs a range of functions, usually fairly specialized, such as GPS tracking, file synchronization, skinning of front ends, etc.