Stanford University, a beacon of higher education and research, offers a plethora of courses across various fields. Some of these courses are freely available to the public, providing invaluable knowledge to learners worldwide. Here is a list of 20 of the best free Stanford courses you can enroll in:

1. Machine Learning: This course provides a broad introduction to machine learning, datamining, and statistical pattern recognition.

2. Algorithms: Design and Analysis: Learn about algorithms and data structures that power your applications.

3. Introduction to Mathematical Thinking: Develop your mathematical critical thinking and proof techniques.

4. Cryptography: Understand the cryptographic underpinnings of digital security.

5. Computer Science 101: An entry-level course teaching the basics of computer science for a broad audience.

6. Human-Computer Interaction: Explore how human users interact with computers and design software that improves this interaction.

7. Game Theory: Learn the mathematical modeling of strategic interaction among rational decision-makers.

8. Probabilistic Graphical Models: Dive into probabilistic models that provide algorithms for discovering patterns in data.

9. Natural Language Processing with Deep Learning: Get introduced to the exciting world of interpreting human language with AI.

10. Databases: Gain a solid understanding of database system concepts.

11. Neuroscience for Beginners: A course providing the basics of how our brain functions from a biological standpoint.

12. Self-Driving Cars with Duckietown: Enter the world of autonomous vehicles and control theory.

13. Health Across the Gender Spectrum: Understand health issues unique to the LGBTQ+ community.

14. Child Nutrition and Cooking: Gain insight into healthful eating habits and how to construct a proper diet for children’s developmental stages.

15. Social and Economic Networks: Models and Analysis: Learn how networks are used to model social and economic phenomena.

16. Startup Entrepreneurship Specialization: Get an inside look at how Silicon Valley startups begin their journey.

17. Writing in the Sciences: Enhance your writing skills with a focus on clarity, precision, and efficiency in scientific contexts.

18. Statistics in Medicine: A beginner-friendly introduction to statistics through medical examples.

19. Understanding Einstein: The Special Theory of Relativity: Delve into one of the most profound scientific ideas of the 20th century.

20. International Women’s Health and Human Rights: An overview on women’s health issues globally, across varying socioeconomic backgrounds.

These courses present an incredible opportunity for anyone looking to expand their knowledge base or delve into new subject matter areas without financial barriers – all you need is Internet access and a thirst for learning!