The TweeTabs project aims the production of yet another Twitter reader, including machinery for personal management of Twitter lists.
This is a young tool: TweeTabs went from pre-alpha to alpha on 2009-05-31. It is usable as a mere Twitter reader and tweet sender. Despite my short supply of free time, it is now fairly likely that TweeTabs will soon become usable as a management tool.
Read the TweeTabs Tutorial to get started (including installation requirements and instructions), and play with the program for a little while. It surely helps being familiar with Twitter already.
Once you got a feel of Tweetabs, you may want to read the TweeTabs Reference for more complete information. This manual is terse, so for becoming a TweeTabs power user, you'll have to read this document slowly enough ☺. On the other hand, don't be afraid of the details, as deep down, this is a rather simple program.
The older TweeTabs as a project sketches what were my intentions before the project even started.
P.S. On a related topic, and relatively more recently, I shared a few Twitter thoughts.