RichEdit.

[ramguru]

Quite a lot actually:
Programmer's Notepad 2 very good IDE (I use it for poasm) http://www.pnotepad.org/
Notepad2 very good editor, I like it because it has lexer for resource files http://www.flos-freeware.ch/notepad2.html
...

[PBrennick]

It says open source, I did not find any source.

EDit:  I found the fource to the second one and I see that it is written in VC.  Sorry, we do assembly here.

Paul

[ramguru]

Do you have an example of it being used as an editor?

Paul

if you mean written in assembler - I haven't any, but I can write one...

[Mincho Georgiev]

I like more 'stand alone' applications  :U :

http://www.masmforum.com/simple/index.php?topic=3942.0