I'm not sure if there is a minecart plugin that does this already, but we were thinking of adding minigames to our server and we came up with the idea of having a minecart mariokart clone, basically having several rails running parallel, and the necessary plugin should be tasked with allowing users to change left-right track. Possibly also allow a donkey kong country-like cart jump when jumping while inside the cart. Is this crazy or I can still hope?
