The IB-Academy.nl Team has assembled a number of great guides for multiple subjects.
They are based in Utrecht, the Netherlands and offer revision courses and tutoring.
These high quality study guides are available for free!
These are published under the Creative Commons
BY-NC-ND 4.0 International License;
which we are complying with:
-by offering attribution;
-not modifying or deriving from them;
-and not using them for commercial purposes.