Tui - Twitter client based on mobile.twitter.com in menu bar. Features:
Tweetbot - Sync your timeline across your iPhone, iPad, and Mac. Mute tweets by user, hashtag, tweet source, or keywords (including regex). 3rd Party support for image, video, read later, and timeline sync services.
Earthquake - Terminal-based Twitter Client with Streaming API support. Only supports Ruby 1.9 and later.
TweetDeck - TweetDeck is your personal browser for staying in touch with what’s happening now.
Cato Social Network - Become Cato. Post Meows, get Not So Anonymous Messages, connect with other Catos & grow your online social network.
HootSuite - Enhance your social media management with Hootsuite, the leading social media dashboard. Manage multiple networks and profiles and measure your campaign results.