VSViewer is a simple program for editing and previewing VapourSynth scripts.
Screenshot: http://i.imgur.com/l7eyPZj.png
Hit F5 to preview. Move around in the preview window using left, right, page down, page up, home, end. Press g to go to a specific frame.
In Linux:
qmake make
Make sure qmake is from Qt4.
VapourSynth revision R20 or newer needed.
Something leaks, maybe 1 megabyte every time a script is (re)loaded.