It's an online free-to-read, donation-supported book on typography. He just linked to the wrong page. Which is described in the page he linked, by the way. In

It's an online free-to-read, donation-supported book on typography. He just linked to the wrong page. Which is described in the page he linked, by the way. Index page link: https://practicaltypography.com/index.html https://practicaltypography.com/index.html Edit: HN is graylisted by the site, presumably due to large numbers of non-paying referrals.