Typography, visual hierarchy, design fundamentals.

Better Web Type. Free typography course on rhythm and hierarchy.
How to Proof a Typeface. Jonathan Hoefler's proofing guide.
Kerning Tool. Kerning typography in Houdini.
NNGroup Visual Design. Research-backed principles on hierarchy, contrast, whitespace.
Practical Typography. Free online book on type fundamentals, hierarchy, spacing.
The Futur. Graphic design fundamentals, typography, grid systems.
Typewolf. Curated typography inspiration. Fonts in real-world use.