Mahjong set (Chinese tiles)
various makers
The best numbers drill anyone has ever built, and it was not built to be one. Every hand forces you to read 一 through 九 and the three suits at speed, dozens of times, under mild competitive pressure — which is precisely the condition under which recognition becomes automatic. It is also the most socially useful thing on this page: mahjong is played across the Chinese-speaking world, and knowing it opens doors that a vocabulary list does not.
What it does not do: The vocabulary it teaches is small and specific — numbers, suits, a handful of calls. You will not learn a sentence from it. Rules vary enormously by region, so expect an argument about scoring with anyone who learned elsewhere.
Free here first: Learn the numbers here first, free