This simple app does exactly what it says -- shows your Windows 8 device's network use over time. It'll appeal to people who are geeks about such things, and to those who pay for mobile connections and want to hold down costs.
You'll see monthly, daily and hourly use, for data both sent and received. You can also compare similar time periods, such as your March 2013 vs. February 2013 usage.
If you use more than one network connection (for example, a Wi-Fi connection, an Ethernet connection and a mobile data connection with a cellular provider such as AT&T), you'll be able to see usage for each. You also get details about the connection, including the IP address, speed, encryption type and more.