More multiplayer with @molatov and @HeroicVillain :
If you want to try it: MPTest.7z - Google Drive
Server: need to click Play, then enter his local ip (often 192.168.X.X) and click on Server
Client: enter Server public IP and click on Connect. Once the game is loaded, enter Server public IP and click on Client
For the server, ports 7777 and 8000 must be open for both TCP and UDP
Controls: Left click to use, left Ctrl to add, mouse scroll to change radius