In the United States, the National Oceanic and Atmospheric Administration provides hourly XML feeds of conditions at 1,800 locations. For example, the feed for a small airport close to where I'm writing this is at http://w1.weather.gov/xml/current_obs/KDTO.xml.
Write an application that fetches this data, parses it, and displays it in a nice format.
(Hint: You might not have to download a library to handle XML parsing.)
See the weather directory for the solution. Here it is run in iex:
I could have used Erlang's xmerl library but chose to use SweetXml instead; it's a nice little wrapper for it.
iex> Weather.check
Weather at Denton Municipal Airport, TX
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Time: 4:53 pm CDT
Temperature: 92.0° F
Winds: 12.7 MPH to the South