João Batalha – https://twitter.com/joao_batalha – and Luís Batalha – https://twitter.com/luismbat – are cofounders of Fermat’s Library – https://fermatslibrary.com/
Fermat’s Library is a platform for annotating papers. Each week they send out a paper annotated by their community. Some recent papers were Birds and Frogs by Freeman Dyson – https://fermatslibrary.com/s/birds-and-frogs – and Von Neumann’s First Computer Program by Donald Knuth – https://fermatslibrary.com/s/von-neumanns-first-computer-program
They’ve also built a Chrome Extension call Librarian – https://fermatslibrary.com/librarian – for the arXiv which allows you to get direct links to references, do BibTeX extraction and make comments on papers.
You can find them at https://fermatslibrary.com/
Read the transcript at https://blog.ycombinator.com/fermats-library-annotating-academic-papers-every-week