It's a small USB to TTL serial tool using the PL2303 chip. You can use it to connect some serial device to your PC via USB port.

Features:

• Compatible with 32-bit & 64-bit Windows Mac OS 8 to OS X Linux and Android!
• To test the unit use the shunt to connect TX and RX (loopback test)
• 3.3V and 5.0V outputs are available to power your project directly from the adapter.