The ATtiny1604 is one of the 'new generation' of microcontrollers from Microchip (née Atmel). It packs a surprisingly large punch into a very small package. But it's available only in surface-mount packages, making it a little tricky to use on breadboard prototypes.

This 2-layer board takes the SOIC-14 chip and turns it into a 15.24mm-wide DIP-16 format.

Yes, you can buy SOIC-to-DIP PCBs easily enough, but this board adds a few quality of life features.

There's a decoupling capacitor on the board, near the IC's power pin.

There's a three-pin header allowing you to program and debug over UPDI with just a common USB-to-UART cable. A diode is provided for this interface.

All the pins are clearly labelled.

The boards are small enough that you can panellise them to gets lots of boards at a very low cost (I used a 4x4 panel).

While the three components (not including header pins) are surface mount, I've chosen packages sizes that are relatively easy to hand-solder and very easy to reflow solder.