Many of you may know that I work at Whitman College and David Guichard, author of the widely used open-source calculus textbook aptly named "Single Variable Calculus", is in my department (in the office right next door).
Not surprisingly, many of us in the dept here use this textbook. Hence, a pdf copy of the textbook sits on one of our dept webservers (https://www.whitman.edu/mathematics/calculus/calculus.pdf).
A couple of days ago Whitman's tech support folks received a DMCA takedown request from Cengage (a commercial textbook operation) for this pdf file. Lest there be any doubt, Cengage does not own the rights to this text. Indeed, on page 2 of the pdf one can view clearly the creative commons license governing the use of this text. Fortunately, our tech services folks have a good sense of humor and told Cengage to "eff off!"
I'd love to post the actual takedown notice, but (surprise!) the fine print at the bottom of the notice prohibits that. It's too bad that these copyright trolling outfits aren't liable for the time and energy consumed by false claims of infringement.
I'd be interested in knowing if other authors of open-source texts have run into this issue.