At Professional Developers Conference 2009, Ray Ozzine, Chief Software Architect at Microsoft, announced Preview of Seesmic, a Twitter Client built on Adobe Air Platform for Windows. Multiple Twitter accounts and Facebook updates appear together in one single, easy-to-follow column.

Various Features of Seesmic are :

• Ability to manage multiple Twitter accounts
• Retweet Feature with a single Click
• URL Shorter next to Tweet Textbox that make posting long URLs much easy
• User Timeline, Replies and Direct messages can be seen at a same time,to add to it it can also add columns of Other twitter account as well.
• Twitter lists can be viewed in Columns more than one list at a time.Create and save searches
• Multiple functionality Over a Twitter User’s Tweet like Retweet,Reply,Direct Message
• Faster performance
• Auto Refresh for updates
• User profile can be viewed in a different panel which is bigger & better
• Drag & Drop facility for Pictures

Although its in preview but still a very promising Twitter client. We found it one of the best so far to manage multiple accounts and it works with Facebook as well.

Download here : http://seesmic.com/desktop.html