Dispersive wiki: http://wiki.math.toronto.edu/DispersiveWiki/index.php/Main_Page
Complexity zoo (if computer science counts): http://qwiki.stanford.edu/index.php/Complexity_Zoo
Deep Inference (from structural proof theory): http://alessio.guglielmi.name/res/cos/
n-lab (category theory): http://ncatlab.org/nlab/show/HomePage
