The Oxford mathematics Moodle has detailed course listings, and most PDFs are not paywalled.
E.g. the 2024 course:
Open University by Ciro Santilli 40 Updated 2025-07-16
Not really dedicated to open source course material, nor to free courses...
The "Open" in its name only made sense in the 60's, when it was founded, nowadays, there isn't much about this institution that is very different compared to traditional Oxbridge. "Cheap more online university" would be a more adequate name for it.
A system that would truly live up to the name "Open" in the year 2020 is the one described at the ideal university by Ciro Santilli.
Wikipedia even says that the initial focus was on broadcasting learning material on television and radio, so what happened to that now that we have an even more powerful on-demand tool called Internet!
They even created their own MOOC website, FutureLearn. But www.freecodecamp.org/news/massive-open-online-courses-started-out-completely-free-but-where-are-they-now-1dd1020f59/ mentions:
The course content is still free to access, but it’s only available for the duration of the course, and for two weeks after it ends.
OMG. God why.
A few open sources at: www.open.edu/openlearn/free-courses. The 5-hour course on particle physics says it all. Stated as of 2023 at www.open.ac.uk/about/open-educational-resources/openlearn/free-learning:
The OU provides around 5% of its formal course materials as free open educational content every year on OpenLearn
www.youtube.com/watch?v=Pj0rbafFBak What's an Open University Degree Like? by Luke Cutforth (2021) mentions that it is more autodidactic/online, and it encourages part time learning.
youtu.be/rsWwffX-u0A?t=99 Open University - How does it work? by Matt Greg Vlogs (2017) shows that they do have their own custom institutional material. And it is not open???? Please. youtu.be/rsWwffX-u0A?t=222 mentions that there is no entry exam, and you can change your courses at any time, that is good at least.
Israel apparently also created their own version in the 70's inspired by the British one: Open University of Israel. Same story it seems.
Group of students that represent students academic views about the courses.
Video 1.
A very honest review of my Oxford University master's degree (theoretical physics at keble college) by alicedoesphysics (2020)
Source. Basically all her courses are from the Mathematical Institute of the University of Oxford, and therefore show up at the Moodle of the Oxford Mathematics Institute of Oxford.
Video 1.
History of Oxford University by Chris Day (2018)
Source. A large part of the video talks about how the insane system of colleges of the University of Oxford came about organically.
I.O.U, Road Games, and Metal Fatigue are also extremely worth it, they are so good that even the singing does not spoil them. s2 forever Allan.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    Figure 3.
    Visual Studio Code extension installation
    .
    Figure 4.
    Visual Studio Code extension tree navigation
    .
    Figure 5.
    Web editor
    . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact