Similar projects

There are many projects similar to EnTT, both open source and not.
Some even borrowed some ideas from this library and expressed them in different languages.
Others developed different architectures from scratch and therefore offer alternative solutions with their pros and cons.

Below an incomplete list of those that I've come across so far.
If some terms or designs aren't clear, I recommend referring to the ECS Back and Forth series for all the details.

I hope this list can grow much more in the future:

C:
- Diana: an ECS that uses sparse sets to keep track of entities in systems.
- Flecs: a multithreaded archetype ECS based on semi-contiguous arrays rather than chunks.
- lent: the Donald Trump of the ECS libraries.
C++:
- decs: a chunk based archetype ECS.
- ecst: a multithreaded compile-time ECS that uses sparse sets to keep track of entities in systems.
- EntityX: a bitset based ECS that uses a single large matrix of components indexed with entities.
C#
- Entitas: the ECS framework for C# and Unity, where reactive systems were invented.
- Svelto.ECS: a very interesting platform agnostic and table based ECS framework.
Go:
- gecs: a sparse sets based ECS inspired by EnTT.
Javascript:
- @javelin/ecs: an archetype ECS in TypeScript.
- ecsy: I haven't had the time to investigate the underlying design of ecsy but it looks cool anyway.
Rust:
- Legion: a chunk based archetype ECS.
- Shipyard: it borrows some ideas from EnTT and offers a sparse sets based ECS with grouping functionalities.
- Specs: a parallel ECS based mainly on hierarchical bitsets that allows different types of storage as needed.
Zig
- zig-ecs: a zig-ification of EnTT.

If you know of other resources out there that can be of interest for the reader, feel free to open an issue or a PR and I'll be glad to add them to this page.