I submitted an article yesterday about its own power-grab regarding bibliographic metadata, "Let the Metadata Wars Begin":
<https://scholarlykitchen.sspnet.org/2022/06/22/oclc-sues-cla...>
<https://news.ycombinator.com/item?id=33556442>
That lists a number of resources:
National Libraries <https://www.dnb.de/EN/Ueber-uns/Presse/ArchivPM2015/metadate...> (linked data: <https://www.loc.gov/item/lcwaN0018834/>)
Harvard <https://hangingtogether.org/harvard-bibliographic-data-relea...>
MetaDoor <https://meli.org.il/wp-content/uploads/2021/12/Chani-Yehuda_...> (from Clarivate, subject of the lawsuit headlining this article)
I'm also aware of the Internet Archive's Open Library (initiated by Aaron Swartz, see below), and some Wikidata efforts based largely on ISBN. And of course the almost wholly useless HathiTrust.
On Open Library data: <https://openlibrary.org/help/faq/using>
Wikipedia Book Sources: <https://en.wikipedia.org/wiki/Special:BookSources/>
There's also the lawsuit by OCLC against Clarivate:
<https://www.infodocket.com/2022/06/15/oclc-files-lawsuit-aga...>
And ... searching "OCLC" in the HN archives turns up numerous other references, including Aaron Swartz (miss you, guy), "Stealing your Library: The OCLC Powergrab":
<https://web.archive.org/web/20081218092812/www.aaronsw.com/w...>
<https://news.ycombinator.com/item?id=362769> (2008)
Algolia search for "OCLC" on HN: <https://hn.algolia.com/?q=oclc>