The 1.0 version of ScreenTopSecret for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. ScreenTopSecret for Mac lies within Design & Photo Tools, more precisely Screen Capture. This free software for Mac OS X was originally developed by Takeshi Ogihara. We recommend checking the downloaded files with any free antivirus.
From the developer:
ScreenTopSecret displays panels to place over opened windows. When recording the screen or having a presentation, you can cover certain areas you want to hide. In addition to solid color panels, there are "stealth type" displaying copies of the background screen, and "mosaic type" displaying mosaic processed background images. You can also display images.
You may want to check out more Mac applications, such as iGrabIt, GrabberWindow or NewTek iVGA for TriCaster, which might be similar to ScreenTopSecret.