Ask HN: Best tools for communicating about versioned code?

Hi HN - does anyone have any recommendations for tools that improve the experience and accuracy of communicating about code? It's useful that GitHub renders code snippets within comments that link to a commit and line range, for example. But it still often feels like a hassle to navigate, gather and share (perma)links to sections of code. As a result I think there are opportunities to improve the quality of discussion about code - perhaps the tools to do that are already out there?