The following pages and posts are tagged with

Core-ESP32 Page Core Field Unit Processor board using an ESP32 Dev Board with Wifi, BLE and a small OLED screen
Core-Locobuffer Page Standalone "locobuffer-style" Loconet interface with I2C expandability using the USB capability of an Arduino Pro Micro
Core-ProMini Page IO4-based Arduino ProMini baseboard
Core-Wemos Page IO4-based ESP8266 Wemos D1 Core Field Processor board with WiFi and I2C
MRCS-BBProMini Page A ProMini in a BBLeo form factor for use on MRCS cpNode
MRCS-cpNode-ProMini Page Arduino ProMini based CMRI node in 2.71" form
MRCS-cpNode-Wemos Page cpNode (2.7" Tyco Rail) processor for MRCS CMRI applications
MRCS-cpNode Page Arduino based CMRI node

You are free to download these files and make your own boards.