The first idea to pop into my head was to build an interface for Twitter that would let you hear your latest tweets by calling in with your phone. It didn't take more than a few hours that night to throw together what would become Tweeter Phone. This was in the days before OAuth, so updating it to use to not require people to enter their Twitter password was the first big feature request I received.
Initially, it used the same layout as this site, but I always wanted it to have its own layout: something light-hearted and appropriate given the casual nature of its usage, toy-like, and immediately obvious what it was and how it should be used. I'm no designer, but I like to pretend now and then, and this particular exercise also gave me a chance to play around with font embedding. The fonts I chose, Folk and Playtime with Hot Toddies, are responsible for most of the site's tone, and lent direction to the rest of the design.
I also took the opportunity to rewrite the site with Sinatra and DataMapper. It was a small site to begin with, and I wanted to further reduce its complexity by stripping it down to the bare minimum. For instance, I forewent the feedback form for a simple link to Twitter with the text area already populated with @tweeterphone.