Although this is a bit off-topic, I would like to advertise this great widget-based plotting library based on Qt. Apparently it is a one-man-project, but fear not, the build quality and documentation is very good. It also comes with a set of easy to understand examples. The library can also export plots as vector or raster images.
I was looking for a C++ based plotting tool for a simulation project, and it turns out that there really aren't too many alternatives. Although I would recommend matplolib for almost all scientific plotting, real time plotting with intensive computations are a bit different.
Here is a screenshot from my simulation:
