Cinderella is a CLI app to manage common open source needs on an Mac OSX. Checkout the link below for more info.

% open http://www.atmos.org/cinderella/

You should be in great shape for contributing to open source on a mac after that.

Check out the smeagol project if you want to modify the recipes

% gem install bundler
% bundle install
% bundle exec rake repackage
% gem push