The following programs are written for computers running RISC OS. These can either be run on a real piece of RISC OS hardware, or on one of its emulators.
VNCViewer, a VNC viewer for RISC OS.
Allows you (With an appropiate VNCServer) to display and use remote desktops on your Risc OS machine. Similar to using an XServer.
I've tested VNCViewer and VNCServe by running VNCServe on my Risc PC, and VNCViewer on my A5000 using PPP over a 19200 serial connection. A bit slow, but it works, and with the correct colours too :)
Further information can be got from Wikipedia.
VNCInput, a VNC input only client for RISC OS.
Similar to VNCViewer above, but only sends mouse and keyboard events to the remote server. Useful when you have two computers side-by-side and don't wish to keep changing keyboards.
Input is switched when you move the mouse off the right hand side of the screen.
RiscX, an X server for RISC OS.
This is an alpha release of RiscX. An X server for RISC OS, allowing you to connect to remote machines and run the various X clients available.