A variety of simple boards are required in support of cabling. These typically convert between the three connector sizes, convert into 0.1" spaced connectors, extend cables, bus cables, and so on. 

Firstly, there are two boards the were already available. The Grove bussed connector board from Seeed (useful primarily for I2C expansion) and the M5 Stack Grove-to-0.1" board. The M5 Stack boards can be purchased from Digikey and are inexpensive. Its a clever design where the 0.1" side can snap off and you then have 4 holes which you can use as you see fit. I took advantage of this feature and stacked two of them, making a tap for connecting my logic analyser. One nice thing about building circuits with modules is that its easy to tap into cables for monitoring signals, kind of like test points being built-in.

The other boards I've made could be partially summarized as convertors between the cable formats. That is, 10-to-2, 10-to-4, and 4-to-2. 

I made a 4-pin merger. For any peripheral device that uses only one signal line and a 4-pin connector (eg a pot), then it might be useful to merge two of these onto one 4-pin cable. That one signal will always be on the first signal pin, and so the merger takes two of these in, and puts one signal onto signal 1 and the other onto signal 2. 

A similar pass-thru board with just two connectors  ought to be created as a cable extender. I've made cable extenders by taking two 4-pin connectors and soldering their pins together, though this is not going to be robust so a board is better. 

I made a board with two 4-pin connectors and resistive dividers to reduce signal voltage, typically to 2/3rds for converting 5V to 3.3V. Its a cheap way to do it, but I think I will make one using proper level shifters. 

Something missing from this collection is a convertor from 4-pin to various 0.1" pitch pinouts. There are many modules available, for sensors, actuators, and so on, that use 0.1" pitch headers, and the pinouts vary. I believe there are 12 permutations of 4 pins to 4 pins. I tried making one with solder jumpers in a matrix, so that any in/out combination was possible. But it was too big. I want the adapter to disappear into the part. 

One approach would be to replace the header pins with a JST XH connector, with 0.1" pitch, then make a special cable with XH on one end and Grove or PH on the other. But that seems painful. I think having a set of very small boards that cover all the useful permutations would be better. Then all of these devices can be converted to be system-compatible.