WiFi Analyzer is a free program for Android devices. This is one of the first programs that I installed on my Fire when I got it. It is an extremely impressive little program. It will show you all of the near by wireless access points, their signal strength, and channel that they operate on. This is extremely useful if you are trying to set up a wireless network for the first time, or attempting to optimize or troubleshoot WiFi connectivity.
I would say that this is a must have app for just about everyone.