It's like lego for electronic circuits:

"littleBits is an opensource library of discrete electronic components pre-assembled in tiny circuit boards. Just as Legos allow you to create complex structures with very little engineering knowledge, littleBits are simple, intuitive, space-sensitive blocks that make prototyping with sophisticated electronics a matter of snapping small magnets together. With a growing number of available modules, littleBits aims to move electronics from late stages of the design process to its earliest ones, and from the hands of experts, to those of artists, makers and designers."

Source: http://www.ayahbdeir.com/littleBits/