If you want the idea of having a text editor for the DS and be quite adventurous about it, you may want to try out the BLARGH Text Editor created by homebrew developer anomalous_underdog. Instead of using the QWERTY keyboard we all know and love, this text editor utilizes the QUONG layout created by John Strout, with hex-shaped keys.

The keyboard may look difficult to use at first glance (blargh!), but let yourself get accustomed to it for some time and it'll eventually become second nature, the QUONG keyboard being optimized for virtual keyboard input. In the latest revision of this text editor, the homebrew developer added placeholder codes for the following text editing functions: cut, copy, paste, home, end, undo, redo, and search.

Since the documentation accompanying the download file doesn't include installation instructions, better make sure that you know what you're doing before trying to installing it to your DS. For all the other necessary information, however, it is recommended that you go over the readme file first.