AdiInviter Pro - The ultimate contacts importer and tell-a-friend system for your website.
Girafi - Get more from your website visitors. Referrals, feedback, e-mails & more.
CloudSponge - Companies from every industry use CloudSponge’s Contact Picker to get access to their users’ address books.
Ambassador - Referral Automation, Made Simple.
OpenInviter - OpenInviter is a free import contacts (addressbook) script from email providers like Mail2World...
Referral Candy - Run a fully automated, customizable and easy to integrate referral program for ecommerce.