Quora has some onerous policies, unfortunately: https://twitter.com/waxpancake/status/453958676529696769

HN is an excellent venue, but is necessarily text oriented, which is an OK tradeoff I think.

My next project after Stack Overflow, Discourse, is an 100% open source, flexible multimedia-friendly discussion system. It's GPL V2 on the code side, but we also tried to codify Creative Commons as the default license in every install, so discussion replies belong to the greater community: https://discourse.org

(Surprisingly, the default content licenses for most discussion software tend to be rather restrictive.)