AffiliateWP - A powerful affiliate marketing solution for WordPress.
Ambassador - Referral Automation, Made Simple.
ReferralMagic - Turn your users and customers into referral magnets.
Referral Candy - Run a fully automated, customizable and easy to integrate referral program for ecommerce.
Echo - Golang HTTP server framework
Viral Loops - Viral Loops is a viral and referral marketing platform to launch ranking competitions, sweepstakes, pre-launch and referral programs.