This graph shows live temperature data from my house. The blue line is the outdoor temperature, measured from a thermometer on my front porch. The green line is the latest forecast for outdoor temperature from the National Weather Service's National Digital Forecast Database.
The graph uses Multigraph and is interactive; you can click and drag the mouse to see other parts of the graph. Hold the SHIFT key down, or use your mouse's scroll wheel, to zoom in or out.
As you move around to expose new parts of the timeline, the graph uses a web service to fetch more data from a database. The database contains data going back to early 2008.
The data in these graphs is from a "1-wire" sensor that is connected to a Raspberry Pi computer that records the sensor values every 5 minutes and uploads it to this web site.