Researchers at the Akishima Laboratories in Japan developed a device that uses waves to write on water:
The device, called AMOEBA (Advanced Multiple Organized Experimental Basin), consists of 50 water wave generators encircling a cylindrical tank 1.6 meters in diameter and 30 cm deep (about the size of a backyard kiddie pool). The wave generators move up and down in controlled motions to simultaneously produce a number of cylindrical waves that act as pixels. The pixels, which measure 10 cm in diameter and 4 cm in height, are combined to form lines and shapes. AMOEBA is capable of spelling out the entire roman alphabet, as well as some simple kanji characters. Each letter or picture remains on the water surface only for a moment, but they can be produced in succession on the surface every 3 seconds.