technologies for remote proctoring / invigilating I'm interested in a video solution (think Zoom) that would allow an
invigilator to see a number of candidates on the screen but which does
not allow candidates to see each other. Are there any such
software?solutions available for this? Obviously, the more mature the
better so that setup for the client side for candidate is simple. If it
was self-hosted then that would be ideal.

I'm aware of online proctoring / invigilating companies (Examity,
ProctorU, TestReach, ProctorExam,...) but they usually either use their
own invigilators or are quite costy.

Somewhat related question here.
As a partial answer, WeBWorK is an open source tool developed by the MAA (homepage here). You can either host it yourself or pay MAA to host it for you. WeBWorK allows for more complicated problems that multiple choice and automatically can give different numbers for problems (e.g., you might get add 2 + 3 and I would get add 5 + 1). 

This would help with homework and possibly hosting the quizzes and tests (but not the proctoring part). I used WeBWorK when taking an undergraduate-level linear algebra course and found it quite usable as a student (it was actually better than the close-source software that came with my physics book and was used for homework).