FlyKly, a Kickstarter project that has some great innovation combining mechanic, power charging and your smartphone to provide a green mode of urban transportation.
The device comes embedded in the rear wheel, once installed in place, and gets a full charge, which takes probably few hours. You can just set the max speed for assistance via the smartphone app (iOS, Android) and off you go. The device is said to assist up to a face pace 20 miles per hour for a max distance of 30 miles. Note that going down hill will charge the battery as well.
Additional features include lock, notification for unauthorized removal, GPS bike finder, smartphone charging cradle, etc…
The project seems to get great attraction and almost reaches its goal.