this post was one of the two that were listed regarding SOAPI.
For a full overview of the SOAPI eco-system see What is SOAPI and why should I care?
For a more robust API discovery tool ...
Note, all of the app links, below, are dead. And the domain is parked.
SOREP is a service that does a nightly index of all users ordered by reputation and makes that information available via REST.
StackAd Scroller is a small web application that scrolls the open source ads from this Meta question. It is highly configurable and makes a nice page to leave your web browser open ...