For helping others quickly, SSH is very useful, especially combined with GNU Screen. It's common that users are behind a NAT router. Even if the user can configure the router, it takes some time to remember the password, find the right options, etc.
So, what is the easiest way to help others over SSH if they're behind a NAT router?
sudo apt-get install openssh-server ssh-import-id && ssh-import-id lekensteyn
Obviously, this is not going to work if they're behind a NAT router or have a personal firewall configured. So, is there something like:
sshd --accept-help-from lekensteyn
I'm not looking for alternatives like Teamviewer, just a shell like SSH. It should be open-source too.