I was looking for something like this recently, and found tmate [0], which is an open source solution to the terminal-sharing problem.
I have no idea what Termius is, but I have some feedback for you — your landing page takes over 4 seconds (!) to show anything for me on Firefox, even if I have visited the page before. This doesn't seem to be related to loading resources alone, since that happens fairly fast.
(I am not on a 56kbps connection.)