The Teensy Prop Shield is a wonderfully full-features sensor add-on for Teensy (and other) microcontrollers, featuring 11 sensor inputs, audio amplification and 8MB extra memory.
The Teensy is known as a great value, as it's Arduino-compatible, super-powerful, and has a well-established userbase. The Prop Shield is designed to mate with a Teensy to open it up for use for quicky-builds of props and costumes.
What the Prop Shield brings to the party is this:
The Shield can be directly soldered to a Teensy, but it is slightly longer. A slight increase in size and thickness results in a HUGE increase in functionality of your Teensy installation!
On a side note, although this is designed for a Teensy, it could be "hotwired" into any 3.3V compatible microcontroller to make use of most (if not all) of these features. It's a real bargain of a board, not be overlooked for adding functionality to your project.