Multiple accounts with multi-windows.
TweetMarker Support: Timeline syncing of reading position between different Twitter apps.
Inline picture thumbnails for popular services, e.g. Instapaper, Twitter, Yfrog, and more.
Mark Tweets belonging to specific users.
Attach multiple images/videos to tweets.
Image Services: Yfrog, TwitPic, Twitter, CloudApp, Imgly.
Set your own custom Image Upload end point (Must follow the TwitPic API and use JSON).
Video Services: TwitVid, Yfrog, TwitPic, CloudApp.
Read Later (Instapaper & Read It Later) with tweet attribution.
URL Shortening via CloudApp (Default is Twitter).
View/Subscribe to Twitter lists.
Access Twitter lists from user profiles (Lists they created, follow, or followed by)
Direct Messages with conversation view.
Search Twitter and view trends.
Flexible Font sizes (11pt – 20pt).
View users on Favstar, and Twitter websites.
Notifications via Growl and Dock Icon.
Edit your Twitter profile info.
Robust Keyboard controls for navigation and popular tasks.
Other features such as Blocking users and Reporting Spam