After asking a few how-to questions, I managed to put together one of the skins that I was talking about in the help thread.
This skin collects data about all the Mercurial and Git repos on your hard drive, records them to a text file in the skin folder, and then displays that text in a meter.
Download it here: https://bitbucket.org/bjmiller01/rainmeter-skins-reporeport
Most of the heavy lifting is being done by powershell. If you're going to be doing any complicated scripting in Windows, powershell is a good way to go.
There are two entries in the [Variables] section of the skin file that affect how the script works. These aren't used by Rainmeter, but the skin file is read by the script, and that's where those values are used. I strongly suggest that you keep all of your repos within one place in your user directory, and set your "ProjectPath" variable to that. (Remember to backwhack spaces!) That will make the script run *much* faster.
Before you ask: The whole thing is one meter, and thus one block of uniform text. It would be nice to get the color output from Git or Mercurial, but that's not realistic. You need a separate meter for every color change. (I'd love for multiple colors within one meter, in a future version of Rainmeter.

Lastly, this is a public project, MIT licensed. So, please feel free to copy or fork it, and have fun with it. I also accept pull requests. (Subject to my judgement, of course.

Happy new year!