Company Ginkgo Academy created these great apps:
Ginkgo Memory & Brain Training, Chinese characters | HSK 1, Chinese HSK 2 | Ginkgo cards, Chinese measure words | Ginkgo, Ginkgo: Learn Chinese Mandarin, Chinese characters | HSK 3, Ginkgo Geography & World Flags, Ginkgo: History of the World, Ginkgo Art History & Paintings, Ginkgo: Learn French Language, and others..
