This is a booklet published by National Semiconductor that lists many applications for their various "quad" - 4 circuits in one chip - devices.

Voltage Controlled Oscillators, up-down staircase generator, time delays, limit comparators, and so on, all made with quads containing amplifiers or comparators. Here is a new concept of not only using the advantages shown for the digital world, but the ability to use simple quad linear devices to build more complex circuits.