Zenity - Zenity is a tool that allows you to display GTK dialog boxes in commandline and shell scripts.
HTML-Notepad - HTML WYSIWYG editor for structured documents
Yad - Yad (yet another dialog) is a fork of Zenity with many improvements, such as custom buttons...
Notepadqq - Notepadqq is a linux clone (identical application) of Notepad++
Glade - Glade is a RAD tool to enable quick & easy development of user interfaces for the GTK+ toolkit...
TED Notepad - TED Notepad is a portable text editor software that deals with a large variety of text processing tools, supplemental text clipboards, high accessibility through hotkeys, and a customizable number of settings and options.