This is a development board for NXP KW41Z with an onboard 3-24 V input voltage regulator, PCB trace antenna, and JTAG/SWD header. The form factor and pinout match that of an Arduino-pro-mini.
The MKW41Z256VHT4 has a Cortex-M0+ with 256KB flash, 64KB ram, and a dual-mac 2.4GHz transceiver that supports 802.15.4 and BLE.
On the rear side is a footprint to add SMTU2032-LF for CR2032 battery operation. The battery life can be up to several years but power management isn't yet implemented in the RIOT port.
These come with no bootloader and must be flashed over SWD. They'll come programmed with some working RIOT example.
Support in RIOT for kw41z is very recently being added. Currently there are pull requests to add support for the platform and the radio which are usable and may be close to merging. If you intend to use RIOT on this as I do, you must expect to do some RIOT development to get things working currently.