Oxford University Press offers ZIP downloads for various levels of their "American English File" series. These include grammar-related mind maps and teaching packs.

: Comprehensive Grammar Practice Worksheets are available through National Geographic Learning's student site. 🏛️ Classic & Academic Texts

: Classic works like " An English Grammar " by Baskervill and Sewell can be downloaded through Project Gutenberg .

: A seminal 1940 study on the grammatical structure of American English, available for download at Internet Archive .