tpad (Tcl pad) is a WinXP (TM) Notepad enhanced clone entirely written in Tcl/Tk. It requires at least Tcl/Tk-8.4 and it's distributed in source format as a wish(1) shell script and a library named tpad. It's goal is to be as similar as possibile to Notepad, with a most notable exception: tpad doesn't limit the size of the file to edit as Notepad does 8-) Also adding new features isn't prohibited because tpad is subject to the GNU General Public Licence.
Currently it has an Ascii table, a tip database, a simple plugin system and support for regular expressions. There are three plugins implemented: a text formatter, an XML well-formness checker and an HTML validator and corrector, respectively based on fmt(1), xmlwf(1) and tidy(1).
tpad is part of the FreeBSD port collection under the category editors. It is also packaged for common Linux distros and even runs under Windows.