Yes it is a direct clone from the earlier NoMachine NX. That was open source, and later they moved to a new closed-source protocol. FreeNX took the earlier one over.
And no it doesn't support Wayland of course. It's an X11 accelerator, the design is heavily connected to the X11 design. It doesn't replace X11's remote display support, it just augments it. Wayland doesn't have that at all so there is no point there.
It basically removes the many round-trips in the protocol that increase latency, by caching values locally. And it can also keep the session alive when disconnected, similar to what termux or screen do for SSH.
