I use PsychoPy to create and deliver visual and auditory stimuli for my research in cognitive neuroscience. It is a well thought out and very useful tool, far superior to the commercial product "Presentation" in its flexibility. It is straightforward to use the library of tools it provides for programming in python to construct displays for cognitive psychology research. With all the power of python available, it is totally and readily extensible as well. The original developer and maintainer, Jon Pierce, is responsive to users' questions and suggestions, and is actively working to improve and extend Psychopy.