Learnist (formerly known as Grockit) has announced that they have reached a million users and have launched an Android-friendly app. Here are more details on the app's launch from TechCrunch. Also, here is my EdLab blog post re: the Learnist launch in May 2012. What do you think of the self-described "Pinterest of Learning?"
From the TechCrunch article listed above:
With its new Android app, Learnist users can embed 40 different types of media in their learn boards, and with the recent launch of “Learnist SmartRSS,” users can now tap into content uploaded from the hundreds of media companies that have created profiles and are now publishing to Learnist.