I decided to make JAREK ZIEMBICKI's AVRSYN. But there were only the schematics and no board layout so I had to make my own. So I started laying it out on eagle but I got on a deadlock due to the fact that I didn't want to make a double sided board. I would etch it myself and double sided boards are a BIG pain in the but (vias and such, alignment etc). So I made it on a perfboard. But before that, I decided that it should be made into discrete modules. One for the microchip, one for the D2A (an R2R resistor ladder type) , one for the midi interface, one for the power supply and one for the switch multiplexer.
Here is the main part. I put pin headers to wherever it would connect to another module and got myself a lot of ribbon cable. The AVR is a really simple design. Only the layout makes it complicated. It can be made by anyone (Even I made one!!!).