RPCEmu Its own disc and settings
Hard disc, CMOS, HostFS folder, screen size, networking, expansion cards: all per machine. Changing one leaves the others exactly as they were.
Machines
As many machines as you have reasons for
A list of machines you choose from at startup, each with its own disc, its own settings and its own hardware. RISC OS 3.71 beside 5.30 beside a nightly build, running at the same time, seeing each other over the network.
Each one its own computer
Separate in the ways that matter
Create, clone and delete
Clone a machine you have set up carefully and try something on the copy. Delete the copy afterwards and nothing else notices.
Several at once
One machine per process, which is not a workaround but the reason it works: nothing is shared between them by accident, so one wedging cannot take another with it.
Switch without restarting
Recent machines are a menu away, so moving between them does not mean going back to the beginning.
Stopping and starting
Put it down mid-sentence and pick it up tomorrow
The complete running state goes to disc: processor, memory, video memory, devices and the network with it. Restoring puts the machine back exactly, not approximately.
Named snapshots
Save a state, carry on, and come back to it. Useful for keeping a machine at a known point before trying something to it.
Suspend and resume
Save and quit in one action, and the machine's entry in the selector offers to resume. The desktop comes back with the windows where you left them.
From the command line too
Start straight into a named machine and resume its state without touching the interface, which is what makes it scriptable.