Twhirl requires Adobe AIR to run, and features a crowded interface with the usual Twitter options. The default interface has very small text and even smaller buttons.
These drawbacks are tempered by the fact that Twhirl has a lot that can be customized. You can change fonts, colors, and so on. You can even choose from many themes.
Get Twhirl
Related: Missing Fonts iWorks, How to install fonts?, Removing/Disabling Fonts?, iMovie Themes and Titles, How to Import fonts into Font Book.
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