My favourite part about Github are the discussions. Like Twitter, Github allows you to watch the comments and code of well known software developers and have a pick of their way of thinking. The code is interesting, but a lot of times the code lacks the WHY. Why the team or the developer chose to use a pattern or a design or why a feature made it to a language or not.
You can see how big projects evolved thanks to issues, commits and PRs, and you can even participate in the debates and of course in the code. Before Github, all this information was in projects' newsletters, forums, chats... The information was more difficult to find and it would last less.
Promises are not monads Promises could have been very different if it wasn't for some opinionated developers that really wanted them to be like they are.
Promisify/awaitable in node Another one about promises and why the promisify function was added to node.
Immutable issue about typescript Discussion of ways of creating immutable data structures that work with typescript.
Browserify and webpack Browserify can do most of what webpack does, and even more in some cases, great gist and good discussion about the two tools.
One line modules Sindre Sorhus about one line modules and why npm made the "utils scripts" folders irrelevant.