Wikids - An encyclopedia that talks to your kids
Mochi - Write notes and flashcards with Markdown and study them with spaced repetition.
DragonBox Numbers - Teach kids about numbers with an easy and fun game
Yak Tack - remember. words.
Four Seconds - A timer and a simple rule: stop it at exactly four seconds.
Zorbi - Spaced-Repetition Flashcards - Other tools are built by boomers, Zorbi is built by students.