Word Sprint is a free 60-second time-attack game covering 100 essential first-year Japanese high-school English words. Racing the clock turns vocabulary from something you recall into something that fires by reflex.
Quiz content is in Japanese (the interface is in English), so it doubles as fun practice for Japanese learners. No install needed — it runs right in your browser.
Answer the same question correctly twice and it graduates into a mastery card; the ranking counts how many cards you have collected. You can drill only the questions you got wrong, and every day you play adds a study stamp. No sign-up is required and your records stay on your own device. (The questions themselves are in Japanese.)