Open Source - Editors
http://www.nedit.org/
NEdit is a multi-purpose text editor for the X Window System, which combines a standard, easy to use, graphical user interface with the thorough functionality and stability required by users who edit text eight hours a day. It provides intensive support for development in a wide variety of languages, text processors, and other tools, but at the same time can be used productively by just about anyone who needs to edit text.
http://quanta.kdewebdev.org/
Quanta Plus is a highly stable and feature rich web development environment. The vision with Quanta has always been to start with the best architectural foundations, design for efficient and natural use and enable maximal user extensibility.
http://cssed.sourceforge.net/
This is the home page of cssed a GTK2 application to help create and maintain CSS style sheets for web developing.
cssed is a small developer editor and validator, that tries to ease the CSS editing. It is an Open Source project, it means that you can download the program but also its source.
http://hexedit.sourceforge.net/
HexEdit is a hexadecimal file editor for the Macintosh. The most widely used editor of its kind on the platform, HexEdit can handle file sizes of up to four gigabytes with ease, yet has memory requirements of less than a megabyte (with colour turned off).
http://www.gnome.org/
Gedit is the official text editor of the GNOME desktop environment.