You can clone with
Right now, you cannot install MacRuby from the package installer on a base installation of Mountain Lion unless you disable the Gatekeeper stuff or install from the command line (using /usr/sbin/installer).
So, who wants to get a dev ID for MacRuby and be the signer?
I think this would probably fall to @lrz (?)
You can install by right clicking > open
You can also lift the quarantine first: xattr -d com.apple.quarantine MacRuby\ 0.12.pkg
xattr -d com.apple.quarantine MacRuby\ 0.12.pkg