Quora is a individual-focused question and answer site with an emphasis on tagging. You can follow users, questions and topics. The Quora API is an alpha release made specifically to help developers create browser extensions.
For over a year developers have been asking for an API from Quora, the Q&A site that has recently exploded in popularity. The company had been waiting until there were "enough users and content on Quora." A browser extension outed the interface and now there is an officially released, but still alpha Quora API.