The Lanting Xu (also known as Lanting JiXu) is the "Preface to the Poems Collected from the Orchid Pavilion", a famous work of calligraphy by the great Chinese calligrapher, in which he described a summer outing at the place called Lanting and composed in year 353. The preface consists of 324 Chinese characters, and it is the most well-known and well-copied pieces of calligraphy in Chinese history.
This app allows you to learn this great calligraphy, preview the work on either 6-character or single character or full calligrapher(of course, you can do zoom in and zoom out in that way). and write the traditional style form of Chinese simply on your devices. Flip through words and trace the words with your fingers.