tmate is a fork of tmux that gives you a shareable SSH connection string, handy for pairing or remote support. It can coexist with tmux on the same machine.

tmate                              # starts a session and prints ssh and web URLs
tmate show-messages                # show the connection strings again
tmate display -p '#{tmate_ssh}'    # print the read-write SSH command
tmate display -p '#{tmate_ssh_ro}' # read-only link to hand to observers

Whoever has the link can see (or, with read-write, use) your shell, and the traffic passes through tmate's relay servers unless you run your own. Only share on trust, prefer read-only links, and close the session when done (exit). Compare screen.