A few years ago I had a friend visiting Iran who wanted unrestricted access to sites. I didn't have any personal Linux servers on the internet at the time, but I did have a Windows one with Remote Desktop licenses.

It turned out that RDP actually worked pretty well. I did hesitate to post this in case it's seen by the wrong people(!), though given it's a while since it was necessary to use, it may be blocked by now anyway.

I wonder if it was available because it was relatively little known and, if so, what other little known protocols might be available.