Magit-Popup
This package implements a generic interface for toggling switches and setting options and then invoking an Emacs command which does something with these arguments. The prototypical use is for the command to call an external process, passing on the arguments as command line arguments. But this is only one of many possible uses (though the one this library is optimized for).
Magit still used Magit-Popup but is going to be switch to a cleaner and more flexible implementation, once that has been written. Even after that Magit-Popup will remain available and receive bug fixes, so that third-party packages can continue to use it.