Ruber is a fully modular IDE for ruby written in ruby using korundum, the KDE
It works on Linux (and should work on other Unix-like systems).
Except for the basic infrastructure, all of Ruber’s functionality is provided by
plugins. This means that any user can easily augment Ruber’s features by writing
his own plugin. He can also replace functionality provided by the plugins coming
with Ruber in a way which integrates seamlessly with Ruber itself.
Ruber is written in ruby, and so, of course, are its plugins. This means that its
users already know the language needed to extend it. A very different situation
from, for example, Netbeans where you’d need to learn Java to write a plugin for
programming in ruby (in other aspects, Netbeans is a good IDE, with very nice plugins
for developing in ruby).
Ruber uses the wonderful KDE ruby bindings,
which makes it expecially suitable for people using a KDE desktop (but can be
enjoied also by users with a different desktop). In particular, Ruber makes use
of the excellent Kate part for the editor window, meaning it has the extremely
well-written ruby syntax highlighter and most of the tools Kate itself has.