The most popular Eurorack module is Make Noise's MATHS, which is sometimes described as an analog computer. Some years ago, synth YouTuber loopop did a video about the module, starting by breaking down the basic functions into three parts: attenuverting, mixing, and slew rate limiting. Attenuverting is a portmanteau of "attenuating" — turning down — and "inverting"; mixing combines signals by adding them together; slew rate limiting is slowing down the rate of change of a signal, making it rise or fall more slowly. By combining these functions (and the extra features Make Noise included), loopop demonstrated about 22 different things a MATHS can do, from basic envelope generation to LFOs to sidechaining to even acting as an audio filter or VCA.
I don't have a MATHS; it's a bit too pricey for my budget (though it's by no means the most expensive of Make Noise's many desirable modules). I have instead a home-built combination of three modules: two copies of Voxmachina's Sigma function and slew generator and a three-channel mixer of my own design, with attenuverters on two of those input channels. And when I just rewatched that loopop video, it turns out my setup can do all but three of those 22 functions, because my mixer doesn't have an analog OR output or a separate inverted output. Which is not too bad for a much lower price point and the satisfaction of saying I made it myself.
(I've gone through some MATHS cookbooks before to translate their patches to a dual Sigma setup, and there are, of course, a couple of other features that MATHS provides and my setup lacks. The MATHS slew channels have independent and simultaneous CV control over rise, fall, and "both", where Sigma provides the equivalent of a "both" and a switchable CV input over one of those; in MATHS, the slope shape, from exponential through linear to logarithmic, is selectable without self-patching; there isn't a gate input to control cycling; and MATHS channel 1 has an "end of rise" trigger instead of the "end of cycle" one that channel 4 or Sigma provides. The kinds of patches that require one or more of the missing features aren't enough to make me desperate to upgrade, but they'd be nice. Replacing the mini mixer with a larger version with attenuverters on each input and an OR out is in the medium-term plans.)
loopop did a follow-up video about using a MATHS to duplicate the dual-suboscillator function of the then-unreleased Moog Subharmonicon, and it turns out my setup can do that too — I was just listening to my system rigged to divide down a VCO signal with the Sigmas, to create random chords from a single note.
