Take a look at MacRuby, RubyMotion, or PyObjC.
For programming in Ruby, MacRuby is the open source version and precursor to RubyMotion (which recently added support for Mac development).
For programming in Python, take a look at PyObjC. PyObjC is a wrapper while MacRuby and RubyMotion are built directly on top of the objective-c runtime, so they will be more performant than PyObjC.