Fixed region screen capture on Mac OS X?

I use both Windows and Mac OS X on my work/home computers, and on Windows I love SnagIt, because it allows me to capture fixed regions of the screen: I select a resolution (for example, 500x400), and then when I click on the capture button a rectangle with that fixed dimensions appears on the screen. I only have to move it to the exact location of the screen where I want to make the capture and it's done.

The capture utilities that I've used on Mac OS X (native, or Jing, for example) doesn't have this feature afaik.

Is there some way to have this kind of feature in Mac OS X? Any utility that could add this to my day-to-day?

The free screen capture tools built into QuickTime and the OS will allow you to take full screen video capture as well as partial captures. You can then edit these down using preview and iMovie to crop and adjust them. This takes time, so there is room for some inexpensive apps that help you by pre-defining the capture area so you don't have to edit down a larger file or worry about being pixel perfect each time you make another capture using the mouse/trackpad.

I use Skitch for static images and used Screeny for video images until Mavericks came out. It doesn't work now, so ScreenFlow is my tool of choice if QuickTime doesn't cut it.

I'm hoping Screeny gets updated since it's lighter and simpler. Nothing will replace ScreenFlow for big projects due to it's post production workflow tools, but you might be well served by a less expensive option or even prefer simplicity over complexity if that's more important than a one time cost.

Skitch is currently free, Screeny is $15 and ScreenFlow $99 - all are available on the Mac App Store.

You can achieve the same result by using advanced editing capacities of ScreenFlow.

ScreenFlow's advanced algorithms only encode areas of change on your screen, so you can capture your entire screen with the highest quality and keep your file sizes low. The ability to capture your whole screen gives you the flexibility to record everything and decide later what to edit out.

You record in fullscreen and then you crop during the post-processing step, handles zoom factor, add mouse overlays etc...
It's a very powerful workflow imo.