Awesome
LiteEntitySystem
Pure C# HighLevel API for multiplayer games using .NET Standard 2.1
Discord chat: 
Features
- .NET Standard 2.1 and pure C# (but with some IL magic)
- Can be used with Unity (2021.2 and later), Godot, Monogame or just pure .net
- Can be used for creation any multiplayer game (2d,3d,4d,...)
- Works with Unity IL2CPP
- Epic speed
- Lag compensation
- Serialization of custom types (like strings,lists,arrays,jsons,etc)
- Synchronized variables (with optional notifications on change)
- Client-side prediction
- Client-side spawn prediction (for projectiles)
- Remote procedure calls (RPC) with compile-time checks
- Client input system
- Basic hierarchy system (childs, parent)
- Controllers and Pawns concept
- Interpolation system
- Delta-compressed state synchronization and input
- LZ4 compression of initial world state
- Also works as game logic engine
- LiteNetLib as default transport, but you can implement any other transport