Invite System For Just Regular WordPress, Not Buddy Press

Is their any program out their that will run on the new wordpress 3.5 for an invite system, as in users can send invites to whom ever they want. Instead of admins adding someone to the site manually???

Thanks
-Dave

P.S.
I’am using Secure Invites and it does work for reg wordpress, granted what it says
https://www.stillbreathing.co.uk/wordpress/wordpress-mu-secure-invites