RPCEmu A port and password per machine
Several machines can run at once, each reachable on its own port, so connecting to one is unambiguous.
Remote
Use it from another computer, or from no computer at all
A VNC server is built in, so a machine can be used from anything with a VNC client. It will also run with no window and no graphical toolkit at all, which is what a server wants.
Over the network
More than a picture of the screen
A control menu, remotely
A key combination brings up a menu over the running machine to reset it or shut the emulator down, so a remote user is not limited to typing at the guest. It is drawn into the VNC display only, so nobody sitting at the machine sees it.
Pick the machine over VNC
Started with no machine named, it offers the machine list over the connection, so a remote emulator does not have to be told on the command line which machine to run.
Reconnect to a desktop session
It is not only for headless use. An ordinary desktop session can be picked up from elsewhere and put down again.
Headless
Genuinely display-less
Not a window you cannot see. No graphical toolkit is initialised at all, so it runs on a server with no display, no X11 and no Wayland session.
That makes a machine something you can leave running: a build target for continuous integration, a ShareFS host for other machines to mount, or simply a RISC OS box that is always there when you want it.
What it is for
A machine that is simply always there
A build machine
Leave a machine running with the guest command line enabled and compile against it from anywhere, including from a continuous integration job that has no display of its own.
A file server for the others
A headless machine hosting ShareFS gives the rest of your machines somewhere to put things, without a window open on your desktop all day.
A RISC OS box on the network
Reach it from a laptop, a tablet or another room. The session carries on between visits because the machine never stopped.
Several at once, each its own
Because the port and password belong to the machine, a host can run a handful of them and each is reachable in its own right rather than through a chooser.