There is VNC client and server software for the Amiga, which should run on OS4 (emulated). But it is an old version and has bugs.
There is no Windows Remote Desktop client for The Amiga to connect to Windows machines (that would be very cool, though, but I doubt it will ever happen).
That is one thing that we really do need desperately. Is more up-to-date software. VNC is just one program I'd like to see updated and properly supported on Amiga. Without good software OS4 won't be fun to use for very long. I really do hope that once OS4 is here the software will follow...