<!DOCTYPE html><HTML><HEAD><META CHARSET="utf-8"><META NAME="viewport" CONTENT="width=device-width, initial-scale=1"><TITLE>Error 500</TITLE></HEAD><BODY><H1>Error 500</H1><P>Internal Server Error</P><p><HR>Powered by <b><i>Abyss Web Server</i></b> X2<br>Copyright © <a href="http://www.aprelium.com">Aprelium</a> - 2001-2017</p></BODY></HTML>
I've been using mongoose to develop JS games offline. It's by far the smallest, simplest server software I've ever seen. Just drop it into the folder you want and run it.
Second to that, I'd recommend Abyss Web Server, which is also free but is more robust than mongoose.
If you know how to computer, you should be able to figure these two out.