Your Mac, from the Mac in your bag or the phone in your pocket
Native apps on macOS and iOS, plus a relay I run myself. One nine-digit ID pairs the two ends — no VPN, no router configuration — and when you are sitting at someone else's machine, a browser gets you in too.
The two ends find each other, even behind NAT.
Usable on a machine where you cannot install anything.
Only the two ends can read the screen or the keystrokes.
Command, Option and the shortcuts you already have in your fingers.