I have made every single one of my flipped videos with Screencastomatic. It is entirely free and while you can set up an account, I never have as it uploads your videos straight into YouTube. The only limitation is that the free version only allows you to create 15 minute videos, but if you are going over that, you are breaking the rules for flipping (since it takes double or more the time to watch and, if necessary, take notes on flipped videos. If you want to see what they look like, you can look at my Playlist.
The video above shows you how to create a video and get going.