The operating system of RevPi Connect is a (customized) Linux based operating system from RaspberryPi foundation. Those operating systems are called, for example, Wheezy or Jessie.
To query the software version and its installation date proceed as follows:
cat /etc/revpi/image-release 2020-06-25-revpi-stretch.img
In this case it is a Stretch operating system from 25th June 2020.