Version 5 of cscrollbar
Updated 2003-01-05 07:25:15A picture is worth a thousand words, so without further delay: 
(Newer versions have 4 arrows (two for the top and the bottom))
License: BSD (Tcl style but copyrighted by GPS)
Platforms: all supported by Tcl/Tk
Download: http://www.xmission.com/~georgeps/cscrollbar/
GPS: Cscrollbar has improved with age. It's the successor to gcscrl. I use it everyday in my editor, and other applications. Stepwise Refinement is what I followed with this (without knowing the specific term until afterwards :). It supports the Tk scrollbar protocol, so every standard Tk widget that supports scrolling can use it. The code is concise, and works well. There is one rough area in the drawing of some gradient colors, but now that I've written new code for Drawing Gradients on a Canvas I should fix this problem soon. It works well for many colors though as is. If you find a feature lacking let me know and I can help, or send me[L1 ] a patch.