The PWM Shield allows you to easily add extra PWM outputs to your Arduino. Each shield has 32 PWM outputs, but you can daisy chain these shields together and get up to 640 outputs! Since they can be externally powered you're not constrained by the amount of power an Arduino can provide either.
You get the assembled PWM shield. It will fit on any board that is pin compatible with an Arduino Duemilanove or Arduino Uno.
If you've ever wanted/needed lots of PWM outputs for your Arduino this shield is what you need. It's easy to stack shields on top of each other and connect them together. All that's needed to add another shield is a jumper wire. You connect the jumper from the first shield to the second shield and you now have 64 PWM outputs.
In addition, you can also change the current of each individual TLC5940 simply by changing a jumper. There are 4 user selectable settings (current calculations can be found in the documentation).
Lastly, for those project that use more power than an Arduino can supply you can externally power this shield. All that's needed to do that is to change a jumper and hook up the external power source.
All documentation including schematics and usage can be found here.
You can also find additional posts about this shield here: posts tagged with PWM Shield