What are the differences between Apache Spark and Apache Flink?
Flink is the Apache renaming of the Stratosphere project from several universities in Berlin. It doesn't have the same industrial foothold and momentum that the Spark project has, but it seems nice, and more mature than, say, Dryad. I'd say it's worth investigating, at least for personal or academic use, but for industrial deployment I'd still prefer Spark, which at this point is battle tested. For a more technical discussion, see this Quora post by committers on both projects.