I really really want to be able to use this without signing up. I just need a link to give a friend so they can spontaneously collaborate with me. The diagram d

I really really want to be able to use this without signing up. I just need a link to give a friend so they can spontaneously collaborate with me. The diagram doesn't need to persist past that session, so long as we can both save a png. The spontaneity and ease of use is a killer feature for me.