Back4App is described as 'open source backend that uses Parse framework and helps developers build scalable and extensible applications at a much more rapid pace' and is an app in the Development category. There are more than 50 alternatives to Back4App for a variety of platforms, including Online / Web-based, Android, iPhone, Windows and Self-Hosted solutions. The best alternative is Firebase, which is free. Other great apps like Back4App are Strapi (Freemium, Open Source), GUN (Free, Open Source), remoteStorage (Free, Open Source) and Nakama (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.
An open protocol for per-user storage OWN YOUR DATA Everything in one place – your place. Use a storage account with a provider you trust, or set up your own storage server. Move house whenever you want. It's your data.
Nakama is an open-source distributed social and realtime server for games and apps. It has a large set of services for users, storage, and realtime communication; as well as specialized APIs like realtime multiplayer, groups/guilds, and chat.
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.
5apps helps both developers and users to get the most out of the Web as a software platform. 5apps Deploy is a turn-key deployment and hosting platform for client-side web apps. 5apps Storage is a new kind of cloud storage for the Web, based on an open protocol.