RareSkills

Speedrun Ethereum is a hands-on series of challenges designed to help you learn by building. Each challenge delivers one key "aha" moment, a mental unlock about how Ethereum really works. At the same time, you'll be building your Ethereum portfolio.

The Ethernaut is OpenZeppelin's browser capture-the-flag: each level is a broken contract you exploit to learn common Solidity vulnerabilities hands-on.

A rich and accessible Web3 toolset for learning, building, and testing on multiple chains

Damn Vulnerable DeFi is a hands-on Ethereum security training environment featuring realistic Solidity and DeFi exploitation challenges.

Explorer is a curated, open database of privacy-preserving tools and guides so builders can compare approaches before picking libraries or workflows.

Updraft is Cyfrin's free, hands-on curriculum for Solidity, security, Foundry, and DeFi: use it when you want structured exercises and certifications before shipping high-risk contracts.