I used to run stunt servers on MTA and later SAMP, so thats what i'll start working on at some point for R:MP too.
Bscly just freemode but the map is packed full of stunt area's, and you earn points and money by doing stunts, that you can then spend on all sorts of things
Before i can do this i need to make (or somebody needs to make) an object streamer though, so i can have 100's to 1000's of objects placed all over the game world without users having to load all of those, they would just have to load the ones within a certain distance, and unload again automatically etc.