Solidity

1. CryptoZombies - a course in tutorial form that walks you through the solidity language and teaches some high level smart contract concepts. This is pretty much the only thing you need to learn the language, but it does not equip you with the ability to think about and design your own contracts.
2. Learn X in Y minutes - one of the fastest ways to get introduced to Solidity
3. Web3 Teacher Training Track by BAF - an intensive six-week training program for aspiring developers and educators in smart contract and dApp development.
4. Intro to Smart Contracts - official documentation for the most widely used smart contract language int he world.
5. Ethereum Developers Resources - A builders manual for Ethereum. By builders, for builders.
6. Consensys Academy - Blockchain Developer Online Bootcamp
7. Common DeFi Contracts
8. Cryptography - In this course you will learn the inner workings of cryptographic systems and how to correctly use them in real-world applications.