If you want to know what motivated me to create TrueShelf (an AI powered adaptive learning platform) and the future of learning, please read my interview on Edsurge.
My Brain is Open
Computational Complexity, Polyhedral Combinatorics, Algorithms and Graph Theory
My Brain is Open 
I am not finding the puzzles i saw in the site two years back . Please keep the old collection archived.
All the (old and new) puzzles are available at http://trueshelf.com/exercises/ and http://trueshelf.com/multi-choices/ We will add a search functionality soon.