A huge majority of them are books, or learning material of some sort. There is learning material on interview practices, or for learning Java, and so on. There is a huge amount of content that is freely available, free as in free speech, creative commons! We are allowed to do whatever we want with them. We can republish them if we wanted for example.
But, unfortunately, it is not easy to remix this content or curate a custom book or learning resource for the specific audiance you are catering to. It can be just for your team, or your students in your class, or maybe even if you want to assign a task to someone, what if you can create a custom one off book containing the relevant information to just perform this task.
For example say I like some chapter from the advanced java
book, and they would need to know some
bits about git so some content from
git-flight-rules, and maybe we
will be deployong in aws so some relevant bits from the open guide to Amazon
But the java book is in PDF form. And the other two are in Markdown. And while
everything is open source, I have license to, and I am sure the authors of those
projects would want me to remix these content, I just do not have a way to take
portions selectively from these projects. Even if the whole thing is not PDF,
and is organised in small markdown files, currently there is no good way to
“remix” these contents.