Diaspora* also has a built in inviter that sends a sign up link via Facebook messaging. Since the one I wrote posts to freinds walls and we do not need invites I am leaving them both in, choose your flavor.
You can now share your aspect lists with others in it.
Weleft.com shut down, I think it sucks, but I also understand when you can not migrate users to the new database what do you do. I update about every day to keep up with code changes so I do not to fall behind.