MGS [2003/04/11] - The text::sync package provides routines for synchronizing two or more Tk text widgets. Synchronization between text widgets can be useful in many situations. For instance, a text editor can have a split view of two different parts of the same document - changes to one text widget are automatically applied to the other text widget. Alternatively, two side-by-side text widgets can be made to scroll together vertically. In essence, any of the text subcommands that affect the content or visual representation of the text widget can be synchronized with other text widgets.

Identifier: text::sync
Version: 0.0.1
Title: A package that enables synchronization between two or more text
Creator: Mark G. Saye <[email protected]>
Description: Provides routines for synchronizing subcommands between
 two or more text widgets.
Rights: BSD
URL: http://www.binarism.com/tk/ 
Available: 2003-04-11
Architecture: tcl
Type: Software
Subject: text synchronization
Language: en

MGS [2003/04/15] - I have included screenshots of the 3 examples at the link above.

Vince says that in Tk 8.5, you can use .text peer create to create two or more sychronized text widgets very easily (but effects like synchronized scrolling require helper code).

See also: