Two dozen mathematicians wrote a 600 page book in 6 months on GitHub
Quibble: I downloaded the pdf, which defaults to a file called 'hott-online.pdf'. Why not Homotopy Type Theory - 1st Edition.pdf'? I download a <i>lot</i> of pdfs (mainly because of being a law nerd), and I am sick to the back teeth of having to rename virtually everything that I download so that I'll be able to find the filename again later. I do use Mendeley to keep my documents more-or-less organized, but what have people got against human-readable filenames? Really I ought to be able to get semantic metadata for everything I download.<p>As for the work itself, great stuff, I look forward to reading it, or at least dipping into it (not a mathematician).