New on Kickstarter: Skallops
Skallops is a new building system by Evan Murphy, Michael Woods, and Marshall Grinstead that uses small laser cut wooden clips to hold together standard playing cards. The clips are designed in such a way as to allow the cards to be connected in as many ways as possible. You can even connect two Skallops to each other back-to-back.
The system is about as simple as it gets, which usually means it has been carefully designed. The project still has a month to go on Kickstarter, but it is already fully funded by a considerable margin.