https://hypothes.is/ https://hypothes.is/ - Maybe relevant to your interests. Very active project. Although IIRC it is scoped to people who use the service and

https://hypothes.is/ https://hypothes.is/ - Maybe relevant to your interests. Very active project. Although IIRC it is scoped to people who use the service and not to your social graph. I follow the project on github and its very active. The volume of problems that they have to solve to make something like this work for users in potentially any environment is pretty astounding.