The USB-I2C dongle is a small device with a form factor much like a USB flash memory. It can be inserted in a PC and then allows the PC to act as an I2C master.
The dongle is used in the evaluation kit of several environmental sensors of ams.
Here you find a user manual, the Windows driver (Windows 7 and 8, not needed for 10), and the firmware for the (micro controller on the) dongle.
The user manual of the USB-I2C dongle describes installation (Windows, Mac, linux), hardware (power, pinning, firmware button), concepts (register and raw model, configuration, transactions, traces), and finally detailed usage (first commands, UART conventions, command reference).