The Start/Stop automata is a security system commonly used in in industrial applications for controlling starting and stopping of operating machines.
The start (run) and the stop command is distributed on two separate buttons, instead of just one switch. Because both in case of startup, both in case of stop for alarm conditions, operator intervention is more immediate, and is directed on the button marked by appropriate color, generally green for Start end red for Stop. Simultaneous pressure on the two buttons determines, for safety reasons, the priority of the stop key and then stopping the device.

Today I write a simple laboratory about a Mealy machine: a circuit that counts forward and backward in a two-bit binary sequence, respectively from 00 to 01 to 10 to 11 and from 11 to 10 to 01 to 00. The state diagram of the counter should look like in the next figure, and if you want to simulate it with JFLAP you can download it through 20151029_Two-bit_binary_up_and_down_counter.jff (to download it click with right button of your mouse on the link and select Save destination...).