This flasher was found in an 80's Electronic Engineering but can be easily implemented with modern general purpose transistors. The frequency depends on C1.
This is 4-input audio mixer using an integrated circuit 741 and two more operational amplifiers....
The CMOS 4060 integrated circuit consists of a frequency divider counter with internal elements...
Found in 90s Popular Electronics, this circuit fires a load through a MOSFET from an audio signal...