Groups as metric spaces: the word metric, quasi-isometry, growth, hyperbolicity, ends, amenability, and the rigidity theorems that recover algebra from coarse geometry.
Free to start · adaptive placement finds your level · reviews timed to your own forgetting.
Every idea is taught with motivation and a worked example before the drills, and an FSRS spaced-repetition engine schedules each review for the day its model predicts you would forget it. A short placement check finds what you already know, so you start Geometric Group Theory exactly where it's useful.