Rapid.io is described as 'cloud-hosted service that allows app developers to build realtime user interfaces without having to worry about the underlying infrastructure. It works as a non-relational data store accessible from client-side code' and is an app in the Development category. There are more than 10 alternatives to Rapid.io for a variety of platforms, including Linux, Mac, Self-Hosted solutions, Windows and Online / Web-based. The best alternative is Firebase, which is free. Other great apps like Rapid.io are Strapi (Freemium, Open Source), GUN (Free, Open Source), Etebase (Free, Open Source) and Supabase (Free, Open Source).
Strapi is the most popular open-source Headless CMS. Strapi gives developers the freedom to use their favorite tools and frameworks while allowing editors to easily manage their content and distribute it anywhere.
Etebase makes it easy to build end-to-end encrypted applications by taking care of the encryption and its related challenges. Think Firebase but encrypted in a way that only your users can access their data.
Kuzzle is a high performance open source, on premise and cloud agnostic backend for IoT and modern apps featuring CRUD, real-time notifications, authentication, geofencing, a full featured cluster mode and more.