Here’s an interesting implementation of a classic: the 555 timer as astable multivibrator for the noble purpose of making weird music. [pratchel] calls this a Morgenflöte or morning flute ...

If you’re not familiar with the 555 timer, suffice it to say that ... Perhaps the most common use is as an astable multivibrator or RC relaxation oscillator. In this role, an external resistor ...