Twitter

Adium
a Multi-Protocol Messenger, supports StatusNet and Identi.ca natively as of version 1.4, as well as good general XMPP support. Multiple StatusNet accounts as well as other microblogging services such...
Apps, Desktop Apps, Mac OS X
chat, Mac OS, multi-system, Twitter
0.25
Annotations
Annotations is a StatusNet Plugin to attach arbitrary custom semantic metadata to notices (like Twitter Annotations, cf. http://dev.twitter.com/pages/annotations_overview).
Plugins, Integration
Annotations, metadata, semantic, Twitter
5
TweetDeck
Supports Status.Net via Twitter Advanced Settings as of v0.34.1. See instructions
Apps, Desktop Apps
multi-system, Twitter
4.666665