yesnoioYou don't need much to build a Retro Module. For a host module (e.g. one that will house the main microcontroller board), you can start with a female DA-15 Connector. Your first client module would use a male DA-15 Connector. Modules don't need to be enclosed.
D-Sub connectors like the DA-15 Connector have three major form factors: solder, removable pins & ribbon crimp. Ribbon crimp connectors, though the most expensive of the three, will save you tons of time.
Solder-type D-Sub connectors are the easiest to find & are the hardiest. They do get to be a bit of a pain as you add more wires to the connector.
Consider starting with removable pin connectors. The pins do not require solder to assemble & are easy to move around if there is a mistake. You'll need a D-Sub pin extractor tool if you want to move pins after they've been installed.
Progress:
This project has been progressing very well, though I am eager to finish the spec & put that part of the project behind me. I have been hampered by minor/major revisions to the spec as much-appreciated feedback has poured in. Revisions cause existing hardware to fall out of compliance -- and the update process is a big pain.
While chainability is certainly a great benefit, I have found greater immediate need of single modules built to keep devices charged and/or route audio to amplifiers/etc. A few of my very-simple afternoon builds see daily use.
It is very tempting to try and fit all the signals I love into every connector I find. This is not possible, and not the best of temptations. Instead, I have sought to identify connectors professionals from various industries prefer & propose things -- where appropriate -- on connetors they would be well familiar with.
My immediate goals are to both wrap up the main part of the specification process, and to finish the retromodules.com website. The site will feature tools which will, via the yaml files in the repository, make the module design/build process faster & easier.
Another common staple of desktop computing is the "AC'97"/"HD Audio" header & breakout modules. Many modern single-board computers feature analog & digital audio, but are often broken out via consumer audio jacks. These small computers could leverage the AC'97 header with great ease -- reducing circuit-board complexity & increasing design flexibility. A source of confusion for many, however, is S/PDIF headers on motherboards. Legacy graphics cards often shipped with a tiny cable for routing digital audio. S/PDIF headers are not well standardized & may consist of two to eight pins. Given this problem, I 
When I decided to make an appearance at Maker Faire, I knew I would need a set of modules to help attract interest. I chose to embed a number of modules into an old flatbed scanner -- along with an Arduino Uno to run everything. The control surface featured all sorts of buttons & fiber-optic-backlit DE-9 & DB-25 connectors. The buttons & LEDs were driven by I2C port expanders & the NeoPixels via the `pixel-bus`. When one (or a few) of the buttons were pressed, the pin holes corresponding to the button label(s) would illuminate. Since I already had a 16x8 I2C LED display, I programmed the Arduino to display button label text there as well. The LED display was behind the scanner glass, while the control surface was mounted on a board well below. The scanner 'display case' and other parts of the display were linked by a single 25 connector ribbon cable. There were other means of input & output as well. Important to the design: I needed certain modules to protected, while others could be messed with. Those goals were well achieved.
engunneer
ronald
novirium
Spring Cleaning! Some reorganization, new things & better documentation. Existing spec is untouched, aside from XLR6: http://retrospec.cc/new