The BlackAdder editor is based on Neil Hodgson's Scintilla editor, which is also available for Linux and Windows as a stand-alone editor, called SciTE (http://www.scintilla.org/SciTE.html).
This editor has a few very nice features. The syntax highlighting for Python (and many other languages) is nearly instantaneous. It also offers auto-indent. This means that you never have to press TAB to indent another level— the editor knows when to indent based on the contents of the previous line.
You can also fold in functions and classes. In the gray vertical bar on the left of the editor pane, there are small horizontal lines, akin to minus signs. These correspond to class, def and other block statements. You can click on the minus sign, and suddenly the whole block disappears under its first line, and a thin line is drawn over the width of the pane, indicating the fold:
Folding in action.
The Scintilla editor component has other interesting features, such as Python tooltips, but these weren't integrated in the beta version of BlackAdder I used to write this book.