It is a modified version of ET_Book called ET_Bembo:

https://github.com/DavidBarts/ET_Bembo

I love u. thanks!

apparently its the font used in Edward Tufte's books. Its on github: https://edwardtufte.github.io/et-book/

The "Quantitative Display of Information", which I just checked, is using Monotype Bembo. So still Bembo, but a different version.

Font is atrocious.

Uppercase letters have different stroke width than lowercase ones — it’s like they are *B*old *L*ike this.

Not only that: tracking, kerning is basically non-existent.

Please don’t use that open-source font

You need real paid Bembo, not that piece of shit.