You can configure it with JS or CoffeeScript, and using JSCocoa gives you access to most (all?) of Cocoa's API to do as you please. And the latest version has a minimal REPL that you can use to tinker.
The author has a nice config you could paste into ~/.windowsapp.coffee to get started:
https://github.com/sdegutis/home/blob/master/.windowsapp.cof...
Here's a link to the CoffeeScript/JavaScript API: https://github.com/sdegutis/windowsapp#api