ViralSweep - Grow your fans and increase sales with sweepstakes and giveaways.
once fyi - Create privacy friendly one-time mailing lists
KingSumo - Grow your audience with viral giveaways that cut marketing costs
Best Referral Programs - A curated directory of startup referral programs
Retweet Picker - Retweet Picker is an online tool that is helping you to select the random winner from Twitter for the giveaways.
Viral Loops for Startups - Virality for startups made easy 💪