I seem to build a lot of Arduino-compatible breadboard projects. I can't help myself. I've been making some boards for myself and others to make things a little easier here and there. They're available on Tindie
First, a better microSD breakout. Better? Well, it plugs right into pins D10-D13. No jumper wires. Power just plugs into the breadboard rails. I call it eeZee microSD. 5V safe, can run off 5V or 3.3V with hinged lid microSD socket.
Second, the eeZee Crystal. This just plugs in next to the XTAL1/XTAL2/GND pins. I made some for me and keep running out.
Also an 8-pin ATtiny target / breakout board as I do a lot of 8-pin ATtiny projects. Programmable with 6-pin ISP header.
Then there's the 20-pin ATtiny target/breakout currently a Tindie Fundraiser
More designs in the pipeline. Please stay tuned. Thanks
Michael