Console

I'd really love to have the ability to open new tabs in an existing window,
much like the way a new tab will open in my existing Firefox window if I
click on a link in another program.

This way I could create a shortcut running something like:
console.exe -t bash -o -r "some command"
(if -o would be the name of the new command line option to reuse an already
opened window)
and get a new tab in an existing window, running bash with some specific
command, or starting in a specific directory. A great example of the latter
would be to add a registry entry on folders like "Open Console2 tab
here..."

If no window was open, a new one should be created, of course. If several
windows were opened, some of them should arbitrary be chosen (the last
active, or the first started, or so). If an already opened window is
chosen, it should probably move to the top, so the user can see where the
tab opened.