Here is a non-electronic relaxation oscillator:

Commentary proposed for NIME Reader

The fingerphone is my creative response to three umbridges: the waste and unsustainability of musical instrument manufacturing practices, the prevailing absence of long historical research to underwrite claims of newness in NIME community projects, and the timbral poverty of the singular, strident sawtooth wavefrom of the Stylophone – the point of departure for the fingerphone instrument design.