The developers of Open Signal on the state of Android in 2015:
We have seen 24,093 distinct devices download our app in the past few months. In our report last year we saw 18,796. In 2013 we saw 11,868.
The horror of developing for 24,093 devices, 1,294 brands, 9 different versions of the Android OS, and an unknown number of variations in CPU, RAM, and screen size combinations sounds— presented in graphical form at Open Signal's website.