[kmfrk]

http://polleverywhere.com have been at this for many years and do a great job of it.

Services like this are particularly good for interaction or feedback in university lectures. Some professors are good at using it to test students in the auditorium to see how many understand the subject.

[goldfeld]

The other day someone linked their service aimed specifically at this problem, https://understoodit.com/

Given that these other general poll services seem to also cover it, not sure if the specificity is good but I think there is a market.

[matteoagosti]

Conferences and lectures are great playgrounds