Analog circuits exist and are widely used in some applications including for stuff like inference in AI models. The issue is that they are somewhat inexact which is a huge problem for most conventional code. As for circuits which work in a discrete rather than continuous space, it's basically always better to just use binary to represent information because 2 states are the most easily separable. Once you have to start separating out more states things get more difficult and it's almost never worth the effort unless you're trying to do stuff like storage in SSDs.