Here's a quick demo of tmate:
The greatness of tmate is that it does not require you to open special ports or install additional software on other peoples machines. All you need is to install tmate on your machine and that the other person connecting has SSH installed and is using a SSH keys.
To install tmate, head on to their site and see the instructions for your distro (including Mac OS). If you plan on starting tmate detached (another post to come with instructions), make sure you install 1.8.10 or above because previous versions did not support this feature.
Git - https://github.com/nviennot/tmate
Official site - http://tmate.io/