ProMicro
ProMicro_LOG 
This module can be mounted to an Arduino Pro Mini, Arduino Nano, Sparkfun Pro Micro, or any other pincompatible MCU running with 3.3V. Depending on assembly it provides a RTC and/or µSD card slot.
Documentation 
All files can be found on Github.
Schematic
BoM
Hardware 
Layout
Gerbers
can be found within the Github repository.
Code 
(unless otherwise stated)
Openlog seems to be tied to Serial0, but ProMicro does use Serial0 for USB and Serial1 internal. Therefore these can not easily be used.