Blockchain
How blockchains, cryptocurrencies and smart contracts work, and where they are useful.
Beginner
Start here. No background needed beyond school maths.
Blockchain and its Applications (IIT Kharagpur)
How blockchains work (consensus, cryptography, smart contracts) and their uses across sectors, with Ethereum and Hyperledger tutorials. Free to learn on NPTEL; the certificate needs a proctored exam with a fee.
NPTEL
Blockchain and Money (MIT)
MIT Sloan course on blockchain technology, cryptocurrencies and their impact on finance and payments, with lecture videos.
MIT OpenCourseWare
Blockchain: Understanding Its Uses and Implications (Linux Foundation)
What blockchain is good for in business, how Hyperledger and other platforms differ, and how to judge a use case. Free to audit on edX; the certificate is paid.
edX