There are many choices for software and many different levels. Firstly you have to decide on what OS you want to use. There is Linux, Apple OS and of course the Microsoft range.
Then there is The software to play your music, play videos, do your navigation and whatever else you may want to do in the car. Now there are some programs out thee called Front Ends, what they do is a combination of Play the music and videos and some of the other functions but also tie in external apps all into a one easier to use application
And then there is those extra programs which do things that the front ends don't.