As far as I know it's the only seriously arc-aware editor in the world - with full syntax highlighting, paren matching, jump-to-definition, delete-surrounding-form, surround-form, expand-macro among others. And it's largely written in arc, so you can use all your arc skillz to customise it.
The catch: it depends on rainbow - http://github.com/conanite/rainbow - and hence on java (the core editor UI is a standard java component) so your enjoyment will depend on having a jdk installed.
