YesGraph - Boost viral growth by recommending who users should invite
Best Referral Programs - A curated directory of startup referral programs
NewsWhip - Chrome extension that checks how viral your content is
Viral Loops - Viral Loops is a viral and referral marketing platform to launch ranking competitions, sweepstakes, pre-launch and referral programs.
Glimpse - Discover trends before they're trending
GrowSurf - Referral software for B2C, FinTech, and SaaS companies.