Do you mean those more or less useless trading cards?
Maniaplanet does not have accomplishments either, if you noticed.

All relevant stuff happens inside Maniaplanet.
By driving well you ear ladder points and skill points and "planets. And this is it pretty much.
The planets can be donated, e.g. on online servers, or to "purchase" skins, models, title packs and other stuff the community creates.

lazy developers