With Twitter reducing its search history to four days, it is a challenge for applications that are dependent on search results, that went not days but even months back. Several applications have taken on the challenge to fill this void and are building search indexes on top of Twitter. Topsy is one of them and it's sharing its results as an API.
Topsy just indexed its 5 billionth Tweet, so it is giving developers access to a lot of data. The Otter API is a REST-based interface to the Topsy Search Engine. Topsy, which claims to be the largest searchable index of content posted on Twitter, is driven by an architecture that spans a cluster of 500 servers and a petabyte of data. It ranks links, photos and tweets by the number and quality of the tweets.
The Otter API makes available to developers some fairly interesting data that has been mined by Topsy. You can find users who have mentioned a term, or look for experts on a particular topic. Topsy's author influence is used to sorts results.
The entire set of Otter API Resources provides a developer, interesting indexes to search for. For example, if I wanted to find out the experts on Mongo DB, I can use the /experts resource of the Otter API. There's no API Key required, so you can dive right in. Here's the Mongo DB example: