In order to properly run the server components, you'll need to have the following:
...though it should be noted that development is largely done in Safari and Google Chrome at the moment with Chrome out performing Safari. The Cappuccino group has a few bugs filed with Apple that will hopefully be addressed in Mountain Lion. The Safari bugs are largely related to resizing the browser window while a Cappuccino app is loaded and visible.
Well, it's not required right now, but it will be once MunkiFace gains the ability to import new installer items. In the meantime, you could technically run the app in a Linux VM as long as the VM has your munki repo mounted to its local filesystem in a fashion that makes it readable to your web server process. But for future proofing, yes, assume that OS X is a requirement.