Gravitational Lensing
Einstein's General Theory of Relativity demonstrates that a large mass can deform spacetime and bend the path of light. So, a very massive object, such as a cluster of galaxies can act as a gravitational lens. When light passes through the cluster from an object lying behind it, the light is... With this program, one can draw images to see the effect of gravitational lensing. ... You can easily test the effects of several parameters by changing them and redrawing the image. ... If the alignment is perfect, the resulting image is an Einstein Ring.
http://www.kwakkelflap.com/files/gravlens.zip - 75Kb - Download - Screenshot

Dark Solar System
In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. According to the theory of relativity, the effect of such a negative pressure is qualitatively similar to a force acting in opposition to gravity at large scales. ... As NASA reports indicate, 70 percent or more of the universe consists of dark energy, about which we know next to nothing. ... This model agrees closely with established cosmological observations. ... At the beginning of March, 2006 the satellite of China National Space Administration, DARKSTAR started...
http://www.iconempire.com/downloads/dark-solar-system.exe - 539Kb - Download - Screenshot