A: I haven't used either of them before, but from their website it looks like Prefinery is focused on Waitlists, while Viral Loops seems to be focused on referrals? It looks like we have a few features in common though, such as referrals, leaderboards, fraud protection etc..

Promo Amp is focused on giveaways. We make it easy for you to run and manage your giveaway. We also have lots of custom actions that you can use to get people who enter your giveaway to complete. We give you a platform to easily draw winners, and sync/export your data to different CRMs.