Free · no signup · interactive
Every lesson on the site, listed below. All of them are free, need no signup, and are built around something you can actually interact with rather than a wall of text.
Gates, boolean simplification and memory, built from the ground up. Start with a single NAND gate and end up with circuits that remember.
The algorithms interviews and coursework keep coming back to, explained with visualisations you can step through one frame at a time.
Prefer to poke at something first? Try the interactive tools or solve a puzzle.