.avi Video Viewer

VLC (from videolan.org) will let you step through a video one frame at a time, using the ‘e’ key (by default). Unfortunately it doesn’t seem to have a similar option to step back one frame - not completely surprising due to the way most digital video formats work (they are only designed to play forwards). But Shift + Left will do a “small reverse” which might help.

If you need the ability to step back one frame at a time, then loading the avi into almost any video editor might be the easiest way.