Small lightweight addon, that mainly focuses on re-skinning chat windows, but also has few additional features.
Re-skin of various chat elements
Tweaks chat tabs
Provides two border styles, but allows you to easly add more
Removes chat buttons
Enables arrow keys in editbox
Automatically scrolls chat to bottom after some inactivity time
Changes timestamp format
Configurable via Lua file
Modify resize buttons
Some form of fading/minimizing mechanism to move chat out of the way when you don't need it
Configurable notice on tabs for incoming messages
Possibly few other minor features present in most other chat addons
Disclaimer: Due to Blizzard chat code that is bit complex and very messy, some parts of this addon do their job in somewhat hackish manner, which sometimes produces unpredictable results. For one, the way chat tabs are now implemented (on ScrollFrame) makes it very hard, to correctly position re-skined elements. This is also visible in default UI where every docked tab after 3rd one is off (vertically) by 1-3 pixels.
In short, don't be surprised it it blows up in your face