Here are a few things I've made in my spare time.
Bookerbus.com
An easy way to set aside chunks of time for meetings and automatically push them to your Google Calendar.
Busroof.com
Write about your friends and see what they write about you.
YC Deals
Offer deals to Y Combinator startups. YC founders can login via Hacker News to see deals available to them.
Patent Pledge (with Garry Tan)
Sign up to the Patent Pledge via twitter