While the Xcode project included in the git repository is set up in almost every way, to use the new security features of Mountain Lion you must create a self-signed certificate to sign both the app and its helper tool. See the images if you have trouble.
Compiling the project now requires ProwlKit (and its minor dependency XMLReader), both of which are available from GitHub. Placeholders exist in the Xcode project, and it should compile without issue so long as the files are available.
Once your certificate is ready, compile normally and place the app (only) in Applications or wherever you wish.