555 Timer as an Astable and Monostable Multivibrator
555 timer IC - Wikipedia
Smallest Discrete Transistor 555 Timer | Hackaday
555 Timer and 741 Op Amp Hoodie – Engineering Swag
TLC551 IC Timer - CMOS 555 with 1V to 15V power, up to 1.8MHz [TLC551CP] : ID 5222 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits
An op-amp made from 555 chips
Op-amp Multivibrator or Op-amp Astable Multivibrator