The Open Movie Editor includes a special Filter called "Node Compositor". This Filter is actually a tool to create totally new Effect Filters, by combining a large number of existing filters into new combinations. This concept is simple, yet powerful, and it is used by other Open Source Tools like Blender, and also by high end commercial tools like Apple Shake.
The concept is actually so popular that there is also literature available, like Steve Wrights "Compositing for Film and Video", which I highly recommend, to get a deeper insight into how a node based compositing programs might be used.
The following graph is an example that can be easily recreated in Open Movie Editor, and what it does is a simple "Green-Screen" Filter, that makes every part of a video that is close to the tone of green as selected in the "Color Distance" Node transparent.
The next graph is even more complicated, but everything it does is separating the video image into three parts, lighter and darker areas, and everything in the middle. The sliders above then make it possible to adjust "Brightness" and "Saturation" for these parts of the image, and through the alpha channels the image is then recombined and sent to the output. The curves are used to create a mask that only lets keeps certain parts of each image.