I want to announce my other plugin here as well (although it released 3 weeks ago, according to wordpress.org plugin directory).

This one was made, to provide your registered users the possibility, to invite oders to your blog, even if the registration is closed.

Currently active functions:

  • invitation sending
  • invitation cards limit per site
  • after activation, the user is logged in automatically
  • after activation, the user can be redirected to a custom URL
  • activation screen is using the same styles as the login screen (if you have customized login screen it will affect the activation screen as well)
  • Dashboard for custom settings Plugins > Invite friends settings
  • i18n support (localized messages)

Find out more about this plugin at WordPress.org Plugin Directory