I was in a class where there were only 15 kids or less (most had multiple parts and things). I know thats a bit more than 10 but since some were pretty much ensemble parts you could probably do it with 10 people. The shows we did are: Lion King (so illegal. XD) The Wiz FAME Urinetown (a lot of the poor people were eliminated and their lines were given to others)
They've also done Pippin, Starmites, Footloose, and Batboy.
People have worked out doing Jekyll & HYDE with a small number of cast - There's essentially 3 leads, 2 featured and the rest kind of are ensemble parts. But you have to work out the ensemble numbers. Not sure if it's legal to do it, but I've seen it done before!