Gregory's Server@humanetech I am also still seeking something in that direction acutally - I was paying for #Conceptboard last year but it I was not happy (especially in terms of easy to use for collabotion) so if you got a tipp :)
Alternative.to for examply only shows very few options: https://alternativeto.net/software/conceptboard/?license=opensource when one looks for #opensource
@sieben_grafik I came to the conclusion that wrt #FOSS nothing like that exists actually, though some projects come close..
But none are at the level that you can say to a random bunch of people "Let's do a quick sticky note session" and without having to explain a lot and people familiarizing with the UI before they are able to participate.