OnTopReplica lets you put a section of any window always-on-top
You know those neat thumbnails that you get when you hover over an icon in the Windows 7 taskbar? Did you ever notice how they're "live" and keep moving when a video is playing in a window that is minimized or otherwise obscured?
OnTopReplica is a neat little tool that takes this functionality and lets you put one of those thumbnails anywhere on your screen, and it can be any size. Once you run it, you select a window, and then you select a region in that window. Once that's done, anything happening in that region of the window will be shown in a large, permanent, always-on-top "thumbnail" that you can place anywhere on the screen.
One thing to note is that it's window-specific. So, let's say you're playing a video in a Firefox tab and select it in OnTopReplica. You now see the video in the always-on-top frame, just like you wanted. However, if you now switch tabs, you suddenly see your Gmail in that same frame, which is far less exciting. You pretty much need to dedicate a single window to whatever it is that you want to put in the frame. Still, it's a very handy way to keep an eye on a video or any other online content.