Borrow another computer's screens
Show your photos on another computer's monitors: a computer that shares the library and has Portman2 open can lend you its screens, once someone there allows it.
It lends its displays and its main window. They appear under Other machines in Screens ▸ Setup.
Asking for a screen
Drag a mode onto one of the other computer's screens. While Multi screen is on, that computer is asked, and a window appears there asking whoever is at it to Allow once, Always allow or Decline. Once allowed, the screen shows your photos in the mode you chose, styled the way you set.
The line under each machine's name says where the request stands: waiting for somebody to allow it, lending and how many screens are showing, stopped, or in use by another machine. Turning Multi screen off closes this computer's screen windows and lets the other machines' screens go.
The other side
On the lending computer, Esc on any lent screen gives it back. Screens ▸ Incoming shows what is being lent and to whom, with Stop, and lists the machines that are always allowed. A computer can be allowed to take the main window as a kiosk, with no plain Esc; holding Esc for three seconds still gives it back.
This needs the LAN server to be running: while it is off, no other machine can reach this one.