>There were several streams of development which naturally influenced each other- broadly:
>Libraries [...]
>Kernel window systems [...]
>Network window systems supporting access to multiple windows from multiple address spaces on multiple machines via a network, starting from work at PARC by Bob Sproull & (if memory serves) Elaine Sonderegger, leading to Andrew, SunDew which became NeWS, and W which became X.
PIXIE was another very early networked user interface system from the University of Cambridge, which ran across the network between a PDP-7 with a Type 340 vector graphics display and light pen, and a Titan (prototype of the Atlas 2) mainframe.
https://en.wikipedia.org/wiki/Titan_(1963_computer)
https://en.wikipedia.org/wiki/PDP-7
David S H Rosenthal's home town is Cambridge, and he was actually a student at Cambridge at the time, and used those same Titan and PDP-7 computers himself! So it's fair to say that PIXIE had a direct influence on his subsequent work on Andrew, X11, and NeWS.
https://en.wikipedia.org/wiki/David_S._H._Rosenthal
Here's a video of the pie menus in PIXIE:
Flight of the PIXIE - Yuja Wang:
https://www.youtube.com/watch?v=jDrqR9XssJI
Neil E. Wiseman, Heinz U. Lemke, John O. Hiles,
PIXIE: A New Approach to Graphical Man-Machine Communication,
Proceedings of 1969 CAD Conference Southampton
IEEE Conference Publication 51, pp. 463–471.
https://www.donhopkins.com/home/documents/PIXIE%20a%20new%20...
David Chapman, Cambridge University Library
https://www.cl.cam.ac.uk/library/archives.html
This film demonstrates an early graphical user interface in use.
It was made in 1969 to accompany a paper entitled “PIXIE: a new approach to
graphical man-machine communication” presented at the 1969 CAD Conference
held in Southampton.
https://www.cl.cam.ac.uk/events/EDSAC99/history.html
1965 [...]
Fifteen years of CAD research, initially led by C.A. Lang, began,
using a PDP 7 and DEC Type 340 display (the first outside
the USA) connected by data-link to the TITAN. It later
involved a highly innovative numerically-controlled
machine for cutting models of metal parts in plastic foam.
1969 [...]
Research on screen editing under Wiseman using the PDP 7.
Digital Equipment Corporation PDP–7/A - S#126
https://www.soemtron.org/pdp7no126systeminfo.html
Software for the Titan/PDP-7 link