Not mentioned in the article is that the Stacks Project is on github <a href="https://github.com/stacks" rel="nofollow">https://github.com/stacks</a><p>I've always thought that math books should in digraph rather than linear form. What would be interesting is to combine this with a wiki. You could have alternate proofs of the same lemma, or even entirely different presentations (starting from different axioms, for instance)