Tonetongue

Phonology
Tonetongue only has tone, and no sounds.

There is a high and low pitch, a rising pitch, a falling pitch, a rise/fall pitch, a fall/rise pitch, a varying pitch, and long versions. Varying pitch only occurs in long form.

Writing System
Tonetongue was originally not written, but Jewish missionaries devised a system for noting the tones in the 19th Century.