VirtualDub, a free video processing utility

[MountainDon]

This isn't exactly a building tool, but it is a useful video effects processing tool and best of all it is free. Windows only.

It can do useful things like rotating a video clip, cropping the frame, changing contrast or brightness, blur, invert, ...

VirtualDub.org

There is also a host of filters that can be added to it for free also.