Brain Pump - Random educational videos. Learn something new.
memordo - Spaced repetition tool to help you retain more knowledge
Tanglet - Tanglet is a single player word finding game based on Boggle.
Harken - Flashcard app using smart repetition to improve your memory
Bushido Bear - Defend your forest against endless waves of evil demons
Zorbi - Spaced-Repetition Flashcards - Other tools are built by boomers, Zorbi is built by students.