ScreenToGif - Record your screen, edit and save as a gif, video or other formats
Free tool for creating screencasts as gif or other files. If you need a very quick demo of how to do something, this looks like a good option.
Feature Comparison - ActivePresenter
ActivePresenter is a screencast/simulation tool with some similar features to Captivate. The free version can do screencasts and export them to WMV, but not simulations in Flash. You can add captions and zoom and pan even with the free version.