In the last years a variety of open-source software packages focusing on visualization of human brain data have evolved. Many of them are designed to be used in a pure academic environment and are optimized for certain tasks or special data. The open source visualization system we introduce here is called OpenWalnut. It is designed and developed to be used by neuroscientists during their research, which enforces the framework to be designed to be very fast and responsive on the one side, but easily extendable on the other side. OpenWalnut is a very application-driven tool and the software is tuned to ease its use. Whereas we introduce OpenWalnut from a user's point of view, we will focus on its architecture and strengths for visualization researchers in an academic environment.