The yellow things in these the above pictures are 3D printed “polypanels” that I’m using as PCB carriers. With enough building blocks, you can snap together anything from simple test rigs to experimental gadgets:
(the sharp-eyed observer might recognize these panels from the mini megamachine, which used MIDI and LED matrix panels 
)
(several sharp-eyed observers have also pointed out that the ones in this picture are in fact red, not yellow 
)