How to add new stuff to Stunt Rally is described in our wiki under Extending.
First, probably easiest, most fun, and also most welcome, is making new tracks.
If you want to create some, be sure to check:
- - Recent (but not latest) description of SR Editor 2.6 is on my website on many pages with images too.
- Some info on SR wiki TrackEditor with links to video tutorials.
- I recommend watching all video chapters (if you never used our editor), even if they are outdated.
If you want your track included in next SR version, you can read and follow these remarks also read this post about my track rating.
Basically the track needs to be of good quality and have various elements (especially if it is long or a stunt track), those then appear in Track menu with icons (e.g. fluids, objects, obstacles, jumps, various loops, pipes, halfpipes, onpipes, etc.). I can edit the track and improve quality or add some more things, but the more of that is done already, the less I need to do and more likely a track will meet requirements.
To be informed about new official tracks, see Changelog and tracks repo commits for new names.
If you want some custom textures for your tracks e.g. for terrain, vegetation, road, sky, etc. check the wiki Materials.
It tells what to put where and what to edit, also (since ver 2.3) everything new has to be added to config/presets.xml (game uses it and editor lists).
Objects (static meshes or dynamic) have their own wiki page: CreateObjects.
Check it to know how to export them from Blender to Ogre and into game.
Lastly, the biggest task, is creating vehicles/cars. Much easier is dealing with ready blender models, and editing them for game, more here: CarModeling.
The latest list of accepted and planned vehicles is here.