Open Technical Writing
Though it is currently limited to my first draft/edition, I have an open-access technical writing textbook, Open Technical Writing. The project represents the culmination of a dream I had as a graduate student, and Lord willing will be continued with a substantial update once my tenure project is complete.
The full downloadable version in PDF can be found here: https://scholarworks.uark.edu/oer/4/
Again, I hope to return to the project for a second, more comprehensive version.