I wanted something to hold the Arduino Uno R3 (in my case, an Elegoo one) along with a breadboard - standard size.
The breadboard I buy have a sticky back which makes a permanent fixture, or you could just hot glue etc.

I've designed this to be printed without supports. X1C handles it just fine.

This is my first upload of my own designs, - I've hung on to lots of others and will slowly add them.