MetaNote – tweak it as much as you need

“MetaNote intends to be the most versatile editor imaginable. Right
click on features in the editor and edit the code behind them. Don’t
like the way ‘Find’ works? — right click on it, and edit the code.
Need a new button in the toolbar? So add it already, with a single
click. Share packs of extensions and macros with other users.
Everything in MetaNote is under your control, effortlessly, at runtime.”

The project is still in its alpha stages, but a really unique approach. The developer is looking for people that like to jump in and help out making it as versatile as possible.

More about it here