Windows.app: Open source OS X window manager atop JSCocoa
github.com
github.com
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