TITLE: Are there any good websites for hosting discussions of mathematical papers?
QUESTION [106 upvotes]: I was wondering if there are any websites out there which 

systematically provide space for the discussion of mathematics articles (particularly those on the arXiv, though not necessarily just those), and 
have a large enough user base to have some hope of having a good discussion (or at least have hope of attracting one in the near future).

Of course, MO is not so far from such a site, but is organized around questions, not papers, which leads to rather different discussion in practice.  Similarly, some blog posts and nLab pages serve this purpose, but are not created systematically.

REPLY [4 votes]: In Peer review 2.0 thread, from 2021, Martin Sleziak suggested to me this ten years old question. So, there is Papers$^\gamma$ with source code under CC0 Public Domain Dedication. It gains the popularity slowly, in an answer to another MO question I explain possible reasons behind this and give more examples of online platforms devoted to paper discussions.
Disclaimer: I'm the founder of http://papers-gamma.link.