This is a stepper motor driver made from a microcontroller (ATtiny261) and a few FETs. Driving a bipolar stepper motor requires an H-bridge but driving a unipolar motor such as the one I salvaged from a fax machine requires only four FETs:
Typically the common end of the coils is tied to GND and the other ends are driven to VDD but this design does it the other way around in order to reduce the component count. Any FETs could be used as long as they can carry the current that the motor will draw and don’t require more than 5V at their gate in order to switch on.
The hardware supports both full stepping and half-stepping. The firmware uses half-stepping but supports full stepping with a trivial change. The hardware would need changes in order to support micro-stepping.