Shoutbox

Just look on Google for "Jscript read write txt file" and you'll get some good articles. Same goes for encryption, which you will want (and maybe even encrypt the source code too so they can't find out the key you used to encrypt and decrypt it).

As for sending variables, it could be done through a web server I guess. When you start playing you both use the same "key" or token etc so you "pair up" and data is sent between the two. That could get complicated though.

This is why my similar game got put on hold for a while.