Stephen Downes

LibreTexts is an "open educational resource (OER) platform" that offers "a trusted, user-friendly environment for faculty to create, customize, and share accessible and interactive educational resources." It's several services bundled into one, including subject-specific libraries (such as social sciences), LibreOne Single Sign On, LibreTexts Academy " providing instructor and institution support", and an OER Remixer. View the source for a lot of this on the LibreTexts GitHub. This is a big project with a lot of resources behind it and is being actively maintained.