Tootfinder

The brand-new 360-or-so-page book "Testing Einstein: One Hundred Years of Experimental #Relativity" is completely open access as a series of PDF files at https://direct.mit.edu/books/oa-edited-volume/6160/Testing-EinsteinOne-Hundred-Years-of-Experimental (and talking about OA science & tech books: at https://www.nasa.gov/history/history-publications-and-resources/nasa-history-series/ NASA has countless more).