Scratch Multiplayer Server in node.js
http-extension is only supported in scratch 2 offline editor.
Load the extension.json by holding shift and pressing File -> Import experimental HTTP extension.
You need to set the variable player on 1 or 2 (the opposite of the other player). This variable is set in the stage.
In start.js you need to edit the ip of the other computer.
You need node.js: http://nodejs.org
You open a terminal and go to the map containing start.js. Start the server with 'node start.js'