This is probably the most useful thing I learned today.
As a ruby newbie, I'm always looking for documentation for stuff, including information on the "gems" -- or little extra programs others have built -- I've installed on my computer. I didn't realize there was a trove of that info actually sitting locally on my computer.
Thanks to a post by Corey Ehmke, I now know how to see it:
You can see what gems are installed on your local system using gem list in Terminal, but did you know that there's an even better way?
Try this instead: gem server
This starts a WEBrick instance running. Fire up the browser of your choice and navigate to localhost:8808. You'll see a page that not only shows a list of the gems that are installed, but also provides quick and easy access to each gem's RDoc [documentation] and home page.
Very cool. Extremely useful.