[ausev] Controller with differential function?

[evehicle4me at hischopsticks.org]

This post seems to have gotten lost somewhere.  I ran across a  
controller on www.alibaba.com that included a differential function,  
i.e. if using a separate motor on the left and right side of the car,  
a way to adjust the speed of each wheel in a turn, i.e. inner wheel  
slower, outer wheel faster.  I can't find the link now :(

Has anyone seen/used one of these?