These are support scripts and files used by other WLAN Pi packages on the RPi4/CM4 platforms.
Previously, some of these files were part of the fpms package. This has now changed and wlanpi-fpms depends on this new standalone wlanpi-common package.
networkinfo scripts deliver features like CDP/LLDP neighbour detection, allow you to display public IP address, check reachability of internet services or blink eth0 LEDs and allow you to trace an unknown Ethernet cable and a switch port it connects to.
After you SSH to WLAN Pi you will notice Tips in the MOTD. More of them can be added in a one-per-line fashion here: /opt/wlanpi-common/motd-tips.txt
Assuming you are using one of the newer images running WLAN Pi OS, you can install or upgrade wlanpi-common by executing sudo apt update && sudo apt install wlanpi-common.