Resources I've Found Insightful

Functional Programming

• Introduction to Haskell: Graham Hutton's YouTube Channel
• Prolog: Markus Triska's Website and YouTube Channel

OCaml

• Functional Reactive Programming with js_of_ocaml
• Michael Ryan Clarkson's YouTube Channel

Object-oriented programming:

• Test-driven Development book: Growing Object Oriented Software, Guided by Tests
• CSharp MassTransit: Chris Patterson's YouTube Channel

Databases

• CMU Database Group YouTube Channel

Visualisation

• Ate Poorthuis's Course on Interactive Data Visualisation

Data Science

• ETH Zurich Lecture notes on Probabilistic Artificial Intelligence

Markdown

• Fabrizio Mussachio's Markdown guide

Networking

WireGuard

• The complete guide to setting up a multi-peer WireGuard VPN

Mathematics

Optimization

• Michel Bierlaire's YouTube Channel

Coding Practice

• Neetcode.io
• Advent Of Code