You could implement some types of multivibrators with NANDs, and oscillators with pretty loose specs, but I'm not sure you could do everything that a 555 could

You could implement some types of multivibrators with NANDs, and oscillators with pretty loose specs, but I'm not sure you could do everything that a 555 could do. The 555 definitely had more precision. But people do forget what could be done with a couple of very simple gates.