Signals and slots in Qt
One of the most basic elements on Qt is signals and slots. They're a non-callback based framework that allows more generic elements in code. This results in more modularized elements that can be reused more easily and run in all platforms. Nonetheless it has a problem and that's the lack of good documentation due to all the recent changes Qt has been suffering. Currently at version 5.5 it has been almost impossible to link them right and I just found how to.