* hypothes.is, obviously 
* also.... [populus viewer](https://github.com/opentower/populus-viewer)? 
  * Matrix seems really really heavyweight for something like that, but I know they've been patiently trying to say it's Not Just Messaging for a very long time. still need to watch [the relevant video](https://www.youtube.com/watch?v=ra5Uqee59n4)
  * I really really really want hypothes.is but p2p or federated, so...