Keen is a new service from Area 120, a group inside Google that makes experimental projects. It's a bit reminiscent of Pinterest in that the main focus of Keen is having you create your own keens that can be about any topic you either want to know more about or are knowledgeable about and wanting to share that knowledge with others.
After you create a keen, like about how to make bread at home, you can add searches, links, photos, and more related to that topic. You can also select "gems", or resources within a keen that you found particularly helpful. You've also got the ability to invite your friends to collaborate on a keen and add their own links and resources.
Of course, this is a Google product, and so there's a dash of machine learning involved. Every keen that you make will utilize Google Search and machine learning to watch the web for helpful content related to your interests. As you add more resources to a keen, Google says the recommendations will get better.
You can also follow keens that other people have made if you're interested in a topic and want to find out more from people that are knowledgeable about it.
"Keen isn’t intended to be a place to spend endless hours browsing," Google explains. "Instead, it’s a home for your interests: a place to grow them, share them with loved ones and find things that will help in making this precious life count."