Courseroot - Biggest online course database on the web
Inbox Creature - A super cute virtual pet, delivered right to your inbox.
Alcamy - Free, open self-learning platform. Learn & teach anything.
HippityPip - Teach phone numbers to kids
CurrencyStack - A free modern currency data API for fintech apps.
Splitwise - Splitwise is a free tool for friends and roommates to track bills and other shared expenses, so that everyone gets paid back. On the web, iPhone, and Android!