This little half-domino shaped/sized squares are actually individual really tiny computers. You build them together to add functionality to whatever pieces you already have.
They each have a bunch of component in them starting with a 20MHz AVR processor and full color OLED screen on the top. Then they have tactile/haptic drivers, a 3-axis accelerometer, built in flash memory, and rechargeable Lithium-Polymer batteries.
For connections they have IR built in, Bluetooth, and then there are expansion ports on the sides of each square allowing you to connect them to other Siftables like Legos. It sounds cool, kind of like digital Picture Frames sounded cool, I just don’t think the implementation is quite there, hopefully Mr. Merrill and Mr. Kalanithi, the two developers of these things, won’t let them be released until they are ready to succeed in the big time.