OgarII

Your friendly agar.io private server recreation.

It supports all current agar.io protocol versions.
It supports handling multiple worlds, all within one instance. Be wary that you can still use up the one CPU core node.js is running on.
It has a minimal memory footprint, and strictly uses uWebSockets for networking.
The code uses JSDoc to specify types. Understanding what the code does is down to your understanding of English.

Notes

Ask all your questions over on the Agar.io Private Servers Discord guild.
Before connecting from agar.io you will need to do core.disableIntegrityChecks(true) in the console.

Make sure you have node.js version 8 or greater.
Make sure you have a C++11 compliant compiler for building uWebSockets.
- If you're on Windows, npm install -g windows-build-tools.
- If you're on GNU/Linux, use your package manager to install a supported C++ compiler such as GCC.
Clone / download the repo.
npm install in /.
cd ./cli/
node index.js

After your first run, OgarII will drop two files in cli/ / working directory: log-settings.json and settings.json.
To change how OgarII runs, modify cli/settings.json.
To change what gets logged, modify cli/log-settings.json.

To create your own commands, check out src/commands/CommandList.js on the command API. To add it to the CLI use ServerHandle.commands.register, and for chat commands use ServerHandle.chatCommands.register.
To create your own gamemodes, inherit src/Gamemode.js's Gamemode abstract class, modify event handling to your wish, then add it with ServerHandle.gamemodes.register before the handle starts.
The ServerHandle class is standalone, which means that you can completely ditch the cli/ folder, require("./src/ServerHandle.js") and do whatever you want with it. OgarII is also available as an npm package for this exact purpose.