Atmega328P I2C Base Board

This is a spinoff from my ESP-12E i2C Base Board. I really like the ease of use and flexibility of this modular design, enabling me to add various "cards" depending on my needs, without having to resort to breadboard. It does however mean that the card with a specific use be designed first though... The initial design featured 4 slots, with a 5th dedicated to the ESP-12E. This card is big though, 10cmx10cm, and not ideal for use in an enclosure. My idea with this particular circuit is a smaller overall footprint, that can be placed into an enclosure together with 2 cards. This PCB was once again well manufactured by PCWWay. Thank you