EntityX is described as 'EC (entity-component) system that uses C++11 features to provide type-safe component management, event delivery, etc. It was built during the creation of a 2D space shooter' and is an app in the Development category. There are four alternatives to EntityX for Self-Hosted solutions, Windows and Linux. The best alternative is Flecs, which is both free and Open Source. Other great apps like EntityX are ECSY (Free, Open Source), EnTT (Free) and Entitas (Free, Open Source).
Gaming meets modern C++ - a fast and reliable entity-component system (ECS) and much more. EnTT is a header-only, tiny and easy to use library for game programming and much more written in modern C++, mainly known for its innovative entity-component-system (ECS) model.