WikiBooks

Started in July 2003, Wikibooks, part of the Wikimedia Foundation, is one of the most popular Wiki sites to gather lots of free textbooks and educational stuff. Wikibooks gives people easy access to free materials, like textbooks and lessons, on many subjects. They follow open content rules, which means anyone can read, edit, and share their materials. Most of what they have is under the Creative Commons Attribution-ShareAlike (CC BY-SA) license.

Inside Wikibooks, users find many subjects to learn about, like math, science, history, stories, programming, and more. Each WikiBook is split into parts or sections, so finding what users seek is simple. Wikibooks works a bit like Wikipedia. Whether they have an account or not, people worldwide can work together to make educational content. This teamwork keeps the materials growing and getting better.

Wikibooks aren't just in one language. They have versions in many languages so that more people can use them. They also make sure everything is accurate and follows their rules. They have volunteers who check and make sure the content is good, just like other Wikimedia projects. Wikibooks connects with other Wikimedia projects like Wikipedia, which makes it easy to find more information on the same topic.

Users can read everything for free online and even download, print, or save the textbooks as PDFs to use offline. Many educators, students, and self-learners find Wikibooks helpful for learning. And it keeps growing because many people work together to add more textbooks and educational stuff.

Official website: https://en.wikibooks.org/wiki/Main_Page