Here are free Bitcoin open-source websites where people can learn different Bitcoin courses:

1. PlanB Network(https://planb.network) – Offers structured Bitcoin education pathways for developers and enthusiasts.

2. Btrust Builders(https://btrust.builders) – Focuses on open-source Bitcoin developer training and mentorship.

3.Chaincode Labs(https://learning.chaincode.com) – Offers technical resources and study guides for Bitcoin development.

4. Bitcoin Dev Kit (BDK)](https://bitcoindevkit.org/) – Provides developer tools and learning resources.

5. My First Bitcoin (Mi Primer Bitcoin)(https://myfirstbitcoin.io/) – Offers beginner-friendly Bitcoin diploma courses (available in multiple languages).

6.Bitcoin Optech(https://bitcoinops.org/en/topics/) – Deep technical content and updates for Bitcoin developers.

7. Bitcoin Design Guide(https://bitcoin.design/guide/) – Focuses on UI/UX principles for Bitcoin applications.

8. Bitcoin Core Docs(https://bitcoincore.org/en/doc/) – Official technical documentation for Bitcoin Core.

9. Learning Bitcoin from the Command Line(https://github.com/BlockchainCommons/Learning-Bitcoin-from-the-Command-Line) – Practical guide for learning Bitcoin operations via terminal.

10. Mastering Bitcoin (by Andreas Antonopoulos)(https://github.com/bitcoinbook/bitcoinbook) – Free, open-source book explaining Bitcoin deeply for devs and non-devs.

All of these are great starting points depending on your skill level (beginner to advanced).