Rtl_power is a tool that allows you to create wide band signal strength heat maps over a long length of time. It works by very quickly hopping across the spectrum, capturing the RTL-SDR bandwidth of about 2 MHz at a time, and then displaying it on a heat map. This is useful for seeing what frequencies are active and at what times.
Usually to obtain a heat map with rtl_power you need to record the data first, and then pass it through a Python program called heatmap.py which creates the heat map image file. Now there is rtl_gopow which is a new program that directly creates a PNG heat map file from an rtl_power sweep. It is currently available for OSX, Linux, Linux ARM, and Windows.
You can download the binary releases here.