I just now found out that a mobile app was NOT required to attend #FOSDEM, and also that the event is apparently over. When I clicked on the chat link a few days ago, I was scared away by the huge: "get the app" message and missed the link at the bottom as a result.

Was this talk recorded? Looking into Matrix is on my TODO list and now I know there is some integration with Jitsi. I'm still not sure what Matrix is, but it seems like more than merely "a chat system"!