This is a blank MiFare Classic key chain fob - often used for electronic locks or customer identification but also found in other systems where a small and easy to carry tag is desired. The tag contains a NXP S50 chip and an antenna, and is passively powered by the reader/writer when placed a couple inches away.
These can be read by almost any 13.56MHz RFID/NFC reader but make sure it can handle MiFare cards as there are a few other encoding standards (like FeLica).
These chips can be written to & store up to 1 KB of data in writeable EEPROM divided into banks, and can handle over 100,000 re-writes. There is also a permanent 4-byte ID burned into the chip that you can use to identify one tag from another - the ID number cannot be changed