Secure Invites is a WordPress plugin that allows you to only allow invited people to sign up.
Fixed security problem for logged-in users Added [inviteform] shortcode
Fixed BuddyPress redirect bug (thanks to Alessandro: http://www.ilbigliettino.com/) Added mini admin report in a dashboard widget Added invite form in a dashboard widget
Fixed bug for new users invite lockout
Fixed incorrect registration links for standard WordPress and BuddyPress sites
Fixed BuddyPress registration bug (thanks to Patrick Neyman: http://patrickneyman.com/). Made the default settings more sensible. Added proper notification for why the invitation button can be disabled.
Fixed bug with secure_invite_user_can_invite() when time limit is 0
Fixed bug with is_site_admin()/is_super_admin()
Fixed bug in MultiSite and MU admin.
Made the plugin work with standard (i.e. not MU or MultiSite) WordPress.
Fixed bug allowing an email address to be repeatedly invited (thanks to Chestnut from http://blog.bng.net for reporting this bug)
Fixed bug reported here: http://wordpress.org/support/topic/411404
Compatibility with WP 3.0, fixed small bugs
Updated plugin URI
Removed Plugin Register
Fixed conflict bug with group invite screen
Fixed bug with automatic BuddyPress integration options
Fixed bug with template tag form (thanks to Rune from http://vixenmagazine.no)
Added Plugin Register code
Added automatic BuddyPress theme integration, added inviter points system, added bulk deletion of invites, added settings presets, added override for special users, fixed bugs
Added registration email URL to settings
Allowed multiple registration URLs to be protected, changed email headers to fix from address bug
Added a support link and donate button
Added HTML comments for reasons why a user cannot send invites to help with troubleshooting
Added stripslashes() to fix display errors (thanks to Mark from http://of-cour.se/ for reporting that)
Disabled invite form if site registrations have been disabled (thanks to Mark of http://of-cour.se/ for the suggestion)
Added limit to the number of invitations a user can send, added secure_invite_form() function for display in a theme page, added deletion of invites for site admins, cleaned up the architecture