Speaking of interesting applications, the Roomba 980 uses an optical tracking sensor in order to improve the accuracy of its mapping -- inconsistently gripping

Speaking of interesting applications, the Roomba 980 uses an optical tracking sensor in order to improve the accuracy of its mapping -- inconsistently gripping wheels make it impossible to navigate accurately on earlier models (hence the "bounce around randomly" approach) but watching the floor move past gives far more accurate positioning data than simply counting wheel rotations.