Notepad++

This works in so far as it starts a new notepad++ process.

It would be nicer to run the existing notepad++ (if there is one), but
with a new window on top.

using -multiInst -nosession
or just -multiInst
both seem to do the same thing

notepad++ -multiInst -nosession

will do it.

Don

Not quite what you are asking for, but the -multiInst command-line option
will open a new N++ window with a blank document. The only difference to
your request is this opens a separate instance of N++, rather than just a
new tab. So you might find it useful.

The request is to have a Windows keyboard shortcut which when used
anywhere (e.g. when notepad++ is minimized and I'm using some other
application) brings up notepad++ with a new empty window, even if it's
already running, without using any mouse gestures.

For that purpose I've asked for a command line exposing that
functionality.

Double-clicking on the non-tab area assumes notepad++ is already the main
window with focus, in which case I could equally just use Ctrl+N. Neither
of these addresses the request

Double click on non-tab area will do it.

Don