Thanks to Twitter I only needed 6 months to discover the existence of the Google Wonder Wheel. It's been there since May, but I only just now learned about it in an article about how children search the web to find out about.
What is it?
The wheel basically resembles a multi-level mindmap, that allows you to see where you are going when following a thread of search results. When you search, next to a list of resulting pages, videos and images you get a small mindmap like image with your query in the middle and a set of links to (groups of) search results around it. When you click a link, another similar wheel is added, but centered around the search term you clicked. The image next to this post shows the image I got after searching for 'domain specific languages' and then clicking 'domain specific modeling' on the wheel.
With each click, the shape of the mindmap changes, showing always the wheel you came from, and the wheel for the term you came from. Next to the wheel, the search results (pages, images, and videos) for the term you clicked are shown, in the familiar way.
I like this idea, and I'll be using it a lot from now on when researching topics of interest. I've been creating my own mindmaps on-and-off for years, although not as structurally as some, and this will only make it easier to do so when collecting input for articles, columns and blog posts.