Bloxorz

Someday games like this will be illegal except for prisoners and the terminally ill. People will pass them around in back alleys. "Psst. Hey, buddy. I've got one guaranteed to make you obsessed for days on end. Hours will vanish in moments. Your brain will gorge on the new challenges while deadlines pass and assignments go undone. You'll love it."

Until then, have you played Bloxorz?

(HT: The entire Internet!)