This is a Feather "Wing" which can be added to any feather board. It works by sending AT commands over the RX/TX pins that are on D0/D1 of the feather board.
The NBIoT wing also has an optional USB port that allows it to be used as a stand-alone serial USB modem from your PC.
The wing features the BC66 modem by Quectel Wireless which features Cat NB1 LTE.
Designed in KiCad, all source files are available on Github