Z Motor Brake by R3D/Adam Haile

Nero has done an awesome video which also automatically enables/disables the brakes! 

This PCB has relays to short the coils of your stepper motor while unpowered, thereby making the shaft much harder to turn. This means that an unpowered stepper has far better "holding torque" than it otherwise would, even when the printer is powered off.

Powering the board through the top left 2 pin header will energise the relays, and allow the stepper to function normally. You could connect this to a programmable pin and automatically lock the coils when the steppers were disabled, should you so desire, but be careful you don't try to lock the coils while the stepper is being driven - it could damage the drivers!

In theory, this could allow for a 2.4 with ungeared Z for those 10k/mm2 accells on Z.

In practice, it would be useful on say, a switchwire where the gantry can drop.