Simple Maze Generator makes little mazes, then tests them to make sure they're solvable. When it finds a good one, it explores it until you hit SPACE. The counter tells you how many bad mazes it found before hitting a good one. If you turn off Turbo Mode (by shift-clicking on the green flag), you can see it build and test the bad mazes, too.
PLEASE MAKE SURE TURBO MODE IS ON! (SHIFT-CLICK the green flag) Unless you decide to turn it off to see every maze tested.