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 circuit was found in an Electronics World of 1966. It has a range of 5 to 25 000 Hz at 1 dB...
This windshield wiper interval switch was found in the April 1990 issue of Radio Electronics...
This circuit for analog video signals was found in the August 1970 issue of Radio Electronics...