DNN can be extended in many ways. There are hundreds (thousands?) of themes, modules, libraries and providers. Some of them are free and open source, others are sold by vendors in the DNN Store.
The great thing about all these extensions is that they do not solely aim at content editors. There is a vast number of modules that help developer create their awesome custom work in a faster method.
Below you find all open source goodies, links to the download pages & source code. If this does not have what you want or need, you can always try the DNN Store or put your request in one of the forums.