Gwoyeu Romatzyh
General Chinese (通字) is a phonetic system he invented to represent the pronunciations of all major varieties of Chinese simultaneously. It is not specifically a romanization system, but two alternate systems: one uses Chinese characters phonetically, as a syllabary, and the other is an alphabetic romanization system with similar sound values and tone spellings to Gwoyeu Romatzyh. Chao also made a contribution to the International Phonetic Alphabet with the Chao tone letters.