Starfish Reviews is a WordPress plugin that allows you to create your own review generation campaigns that run right from your own website. It's pretty easy, really. Just create a funnel in the familiar WP interface, then send that out to your clients, customers, followers, etc.The funnel helps them provide negative feedback to you, or publish positive feedback on the public reviews platform of your choice: Google, Facebook, Yelp, Amazon, TripAdvisor... basically any online review platform.
It's a WordPress plugin. So it's open-source, GPL 2.0 licensed. It runs on PHP and Angular, with some jQuery on the front end.