Anyone know of a good free video editiing software for Windows that I can download to make a kickstarter type demo/ad video?
I really just need to be able to superimpose text/captions, asdd some stock music, edit snippets and make transitions between frames.
Assuming you mean for a PC, Windows Movie Maker does a decent job of popping together clips. Not much control but it’ll do basic transitions and add music.
Avidemux. 
I agreed with above post, Windows movie maker helps you in general video editing, adding music and giving transitions in clips. But it has only few tools, for more tools, we can use Adobe Premier Pro. It supports many video formats, it has various tools for editing video, adding sounds, adding transitions. It can also edit sounds.