Oxford book template (Choquet-Bruhat, Maggiore, Simon,...)
Edit (2): With egreg's recent suggestion, the package is finally up on CTAN!
I'd like to toss my hat in the ring. While it may not be the exact same as the OUP, I made NotesTeX to mimic the OUP's format. Here's how it looks
Edit: Another Example
I hope this helped!
As someone who is connected to the Department of Physics at the relevant university, I can alas tell you that it isn't explicitly public domain. I too think it's great, and would love it to be more freely available. Entirely unofficially I know that it's the pet child of several academics, who have extended it quite thoroughly, and the press were quite surprised at how much it has evolved in the past few years. One can probably approximate something similar with memoir and margin notes, although the large paper formats used by the OUP leave significantly more room for figures than, e.g., A4.