Is there a native/default SHARE or INVITE setting somewhere?

[JTrollerb123]

In browsing my 3.1.3 settings I saw a setting for how many invites a user group can have....but cant find an Invite feature that is included within the default installation package. Can someone point me in the right direction? If there is no default tool for this, what are the various options to get this installed as a hook, etc?

Thanks!