Credit:
It looks like the intent is essentially to celebrate all the amazing and varied third-party apps that make up and enrich the Twitter ecosystem. Twitter mentions Trendsmap, Tweetmeme, and Seesmic in its first round of accolades.
Not unlike the way Twitter chooses to feature some services prominently in the right-hand column of user profiles beneath the username and follower count, the company is also actively giving props to its third-party developer community here.
It's a much more informal "app directory" than something like the recently launched OneForty, but should be interesting for a weekly zeitgeist of what apps and services are on the collective Twitter hive's mind that week.