Hadoop has a vast and vibrant developer community, but many projects in the Hadoop ecosystem have names that don't correlate to their function, making it difficult to figure out what each project does or is used for.
At its core, Hadoop is only made up of HDFS and MapReduce. But people and companies have made contributions that make Hadoop a more complete platform. Some of these ecosystem projects are Apache Foundation Projects (denoted by “A” below), while others are projects that are Apache licensed, but run by a company (“AL” below).
Here's a cheat sheet to help you keep track of Hadoop developments.