If you use app.net (app.net, a paying alternative to twitter, without the ads, the sponsored tweets, etc…), these websites will provide functionalities or informations you may need.
app.net
The Mothership
http://app.phuu.net
Search your followees that are on app.net (Netbot for iOS has the same function).
http://twapp.phuu.net
Cross-post from app.net to Twitter ($5 lifetime).
http://recentusers.com
Shows the last registered users on app.net along with a user count.
http://appnetizens.com
Tons of analytics about app.net.
https://ifttt.com/
Not really an app.net dedicated site, but allows you to create automated tasks with app.net.
https://github.com/appdotnet/api-spec/wiki/Directory-of-third-party-devs-and-apps
Directory of third party devs and apps (Official)