This one can be found right here. 
The writer of the widget says it best right here:
“History
The reason for developing Twitgit is that I find Twitter’s Jabber integration too obtrusive. It’s cool, very slick and very easy to use but it distracts me far too much at work. A Dashboard widget works perfectly in the background, though, so it puts me in control. I can check Twitter at my leisure, without being disturbed by it. I also use an excellent utility for OSX called Dasher; a tool to automatically pull in Dashboard after a specified period if inactivity — like a screensaver. So for me, I’ll come back to my machine with a cup of tea and Twitgit will be sitting open and up to date. I can glance at it to read the latest twitterings, perhaps post quickly, then pop back to work with no further disturbance.“
