TL;DR of the article, generated automatically.

hjkl is a free browser game that teaches Vim by having you make small edits in a real Vim editor.

• What you practice: Motions, text objects, search, marks, counts and repeats, in skills such as changing a word, moving a sentence, finding within a line and jumping through files.
• How it works: Pick the skills you want. Each skill has six edits: two guided, two prompted and two independent. Any valid edit that reaches the target text passes.
• Requirements: No sign-up, and nothing is stored. It needs a desktop browser with a physical keyboard. Type :help in Normal mode for the current commands.

Little edits, lasting skills, as the page puts it.