That's what's nice about certain of the patchable systems...if they're properly done, you have ample choices, plus the expandability into actual modules is built-in and doesn't have to be kludged into working.
Explaining Phenol...OK, back at the beginning of synthesis, Don Buchla's systems wound up all up and down the West Coast at various schools, one of which was CalArts. And there was constant hassles over getting time on the sole Buchla system they had, so Serge Tcherepnin who was an instructor and composer there around 1970 came up with this idea to cook up some basic module boards, parts kits, predrilled panels, and paper panel layouts, and offer these to the students as a project that a number of them could collaborate in building, with the result being that everyone wound up with a few panels which made up a fairly potent patchable synth. These originals actually had no name, and were mostly assembled in an ad-hoc assembly line around a courtyard at CalArts' music department, and wound up being called 'Serge' synths because it was Serge Tcherepnin who cooked the whole project up.
Serge made some changes over Don's designs, though. First off, Serge made his systems more interconnection-friendly. Early Buchlas used all sorts of non-standard voltages and separated the control signals from the audio. Serge changed this so that his modules worked with 1V/8va scaling and positive triggers, and put the audio and control signals back as one single jack group, so that audio could easily be used as CVs, and vice-versa. Second, the actual Serges always tended to follow the form factor that had been used in the first place: modules were mounted onto predrilled aluminum panels, and as these became commercial products, you had to specify which modules you wanted on which custom panels for your system...which is a ROYAL pain in the ass to work with, I assure you!
Now, Andrew Kilpatrick and some other synth builders in the 1990s and 2000s decided to try and do the Serge-type connection format in different ways. Bruce Duncan of Modcan, in his Modcan A systems, created very tall/long modules, and Kilpatrick went more toward Buchla's 4U panels, both using bananas while at the same time, both also did Eurorack development (and Modcan also did their 5U 'B' systems). But it was Ken Stone that worked with Rex Probe and Serge Tcherepnin eventually, after devising some similarly Serge-like modules on his own, and this became Elby, which famously did their 'EuroSerge' form factor...3U with banana jacks.
Why banana jack/plugs? Several reasons, actually...
First of all, the patchcables are lunkhead-simple to make. They don't even require soldering, and you only have a single wire, so it's possible to build piles of patchcables with a wire cutter/stripper and a small adjustment screwdriver (the banana plugs have a setscrew in them that holds the wire in place), and these don't tend to wear out over time. Granted, there have been some people who've griped about crosstalk since the 'ground' is established across the panel, but that's really not a hugely consequental issue for most users.
And second, banana plugs are stackable. This eliminates the need for multiples, and also encourages users to splay signals out in all directions for various purposes, so that one signal source might actually be busy doing numerous things with numerous functions all over the place. Hence why the Phenol is such a potent device, despite it actually seeming rather simple. However, this one 'plus' comes with a big caveat: it is easy to get distracted while patching something complicated and accidentally connect an output to another output. Now, if this happens on a conventional two-conductor jack system, if the outputs don't have diode protection, the result can be damage to one or both modules. But on a banana jack system, a patchcord array that has this output-output patching might be capable of damaging several things at once if the synthesist gets sloppy while programming a patch...say, three outputs get connected. Then you'd run a risk of frying all three outputting modules, and the small instance of overvoltage (if that happens) could also overload and 'pop' any inputting modules in the patchcord array. Icky. But this just means you have to be CAREFUL...which you should be, anyway.
Anyway, banana systems are another compact option on par with Eurorack, inasmuch as there's both prebuilds like the Phenol and a sizable module base. Plus Serge/STS also does their 'shop panel' series, prebuilt panels that, while they cost quite a bit, do astonishing things sonically. The Serge was also sort of the original '0-coast' idea; it had the ability to work with subtractive synthesis to a much greater degree than the Buchlas, but patched in a manner more akin to a Buchla and made use of a touchpad key sequencer like Don's systems tended to.
Anyway, yeah, bananas do look a little...odd. But I have stuff here that uses those as well as loads of other jack formats, and I never see any issues with them. Plus the stackability allows a flexibility you just cannot find easily with typical bipolar connection systems. And if you run out of cables...well, just ring up Mouser or Allied or whatever, get a bag of Pomonas and a roll of 16ga stranded copper wire, then bust out the tools for an evening, and soon enough you'll have a pile of new cables to use. Easy-peasy!