Originally designed for control of HVAC vanes and similar low-demand equipment, these stepper-motor gearboxes have lots of hacking potential. This is the higher-torque / lower speed 64:1 version.
We had some of these drop on our desk a while back with a "You gotta find more of these!" message taped to it. What it turned out to be is a pretty cool, inexpensive geared stepper motor, ideal for a bunch of low-torque applications.
This 28BYJ-48 is a 5V unipolar geared stepper motor, manufacted by the boatload for the HVAC control industry, where you'll find these little units as actuators for airflow control in ducts and vanes. It features a 5mm "Double-D" shaft, mounting lugs, and nice 5-conductor 0.1" pitch connector. The gearing isn't the beefiest or most precise we've ever seen, but it's adequate for reasonable loads.
This version is the 16:1 reduction version (16.032:1, actually), so it's faster and less torquey than it's 64:1 brother.
Being a stepper motor, you'll need a motor driver circuit. There's many ways to drive a stepper, but this ULN2003 driver board is specifically designed to drive these 5V stepper gearmotors.
Thanks to Graham Wideman for his additional in-depth analysis on these gearmotors.