I've made Sansar's first real vehicle prototype.
It's a hover platform that's operated simply by walking around the platform to make it lean in the direction one wants to go.
This machine relies on dynamic stability, especially using a series of PID controllers and the Script API's impulse mechanics. These allow it to respond to changes in mass as people board and move around in order to keep the platform mostly upright and near a target elevation.
There are no hidden collision volumes or other tricks here. This actually works very well, even if Sansar's physics engine isn't perfect.