This is a kalimba

YouTube link.

Thumb pianos traditionally consist of a wooden board to which metal tines of varying lengths are affixed... The longest tines are typically in the center, with shorter (and thus higher-pitched) tines arranged alternately in ascending order towards both sides of the instrument. The thumb piano is most commonly held in both hands, with both thumbs being used to pluck tines either simultaneously or in turn.

Modern variations of the instrument may have more than the traditional array of 15 tines, with as many as four fully chromatic octaves, making the playing of more complex music possible. The thumb pianos are made of different woods, either with only a sound board or often with a resonant chamber. Those with hollow resonating chambers for increased volume, often have two holes on the back that can be used to create a vibrato as the fingers cover and open these holes...

The kalimba appears to have been invented twice in Africa: a wood or bamboo-tined instrument appeared on the west coast of Africa about 3000 years ago, and a metal-tined lamellophones appeared in the Zambezi River valley around 1,300 years ago...

The thumb piano was typically played while walking by traveling griots who keep the history of the tribe or village, and to entertain people...

Much more at the Wikipedia entry.  Seems like the ideal instrument for a generation that texts while walking.