Time Mod
Allows to stop time and advance it frame by frame, useful when debugging logic circuits. Also allows to set a custom speed for the time. On multiplayer only the host can use it.
Controls:
Click the UI button to change between frame advance and change time speed modes
On frame advance mode:
N: Toggle stop time
M: Advance time 1 frame, only works if time is stopped
-: Reset elapsed time counters, only works if time is stopped
On change time speed mode:
N: Toggle custom time speed
Type a number on the UI text box to specify custom time speed
Disclaimer: physics might get a bit weird when advancing time frame by frame.