UserVoice - UserVoice integrates easy-to-use feedback, helpdesk, and knowledge base management tools in one platform that empowers users to speak and companies to understand.

Viral Loops - Viral Loops is a viral and referral marketing platform to launch ranking competitions, sweepstakes, pre-launch and referral programs.

GetSatisfaction - Get Satisfaction is the leading customer engagement platform that helps companies build better relationships with their customers and prospects, through the best online customer community.

Girafi - Get more from your website visitors. Referrals, feedback, e-mails & more.

idea.informer - Idea Informer is a idea forum similar to uservoice or getsatisfaction.

Referral Candy - Run a fully automated, customizable and easy to integrate referral program for ecommerce.