Apache ZooKeeper is an open-source, distributed service for collecting and moving logs. It helps you read, write and observe updates to data in distributed systems.

Apache Pig is a high level scripting language used with Hadoop to simplify MapReduce programming.

Apache Impala is an open-source SQL query engine for processing large volumes of data stored in Hadoop clusters (aka where Hadoop stores its data—HDFS, HBase or even an Amazon S3 bucket).

Apache Hive is a data warehouse software built on top of Hadoop for analyzing data stored in Hadoop clusters. Initially developed by Facebook, Hive is written in Java.

Apache HBase (Hadoop Database) is a NoSQL database that runs on top of the HDFS (Hadoop Distributed File System). It is natively integrated with Hadoop.