An open source distributed database system for storing and managing large amounts of data across commodity servers. It can serve as a real-time data store for online transactional applications and a read-intensive database for large-scale BI systems.  

Apache CloudStack is open source software designed to deploy and manage large networks of virtual machines, as a highly available, highly scalable Infrastructure as a Service (IaaS) cloud computing platform.

Apache CXF is an open source web services framework that helps you build and develop services using frontend programming APIs, like JAX-WS and JAX-RS. These services can speak a variety of protocols such as SOAP, XML/HTTP, RESTful HTTP, or CORBA and work over a variety of transports such as HTTP, JMS or JBI.

Apache Flink is a community-driven open source framework for distributed big data analytics, like Hadoop and Spark. Flink's core is a streaming dataflow engine that provides data distribution, communication, and fault tolerance for distributed computations over data streams.

Apache™ HBase is an open source, non-relational and a distributed database model that runs on top of Hadoop Distributed File System (HDFS). It is column oriented and provides a fault-tolerant way of storing large quantities of sparse data, which are common in many big data use cases. It also adds transactional capabilities to Hadoop, allowing users to conduct updates, inserts and deletes.

Apache JMeter is an open source testing software, designed to load test functional behavior and measure performance. Written in Java, the application is orignally designed to test web applications.

A high-performance, full-featured text search engine library written entirely in Java. It is a technology suitable for nearly any application that requires full-text search, especially cross-platform.

Apache Solr is an open source enterprise search platform from the Apache Lucene project. Its major features include full-text search, hit highlighting, faceted search, dynamic clustering, database integration, and rich document (e.g., Word, PDF) handling. Providing distributed search and index replication, Solr is highly scalable. Solr is the most popular enterprise search engine.

Apache Spark is an open source cluster computer framework used for processing Big Data based on a cluster manager and a distributed storage and in-memory processing model.

One of the Apache big data projects, Spark is a generic engine for analytical big data processing, especially for live streaming data.

Apache Sqoop is a tool designed for efficiently transferring bulk data between Apache Hadoop and structured datastores such as relational databases.One can use Sqoop to import data from external structured datastores into Hadoop Distributed File System or related systems like Hive and HBase. Conversely, Sqoop can be used to extract data from Hadoop and export it to external structured datastores such as relational databases and enterprise data warehouses.

Apache™ Storm is a free and open source distributed real-time computation system for processing of large streams of data quickly. Storm makes it easy to reliably process unbounded streams of data, doing for realtime processing what Hadoop did for batch processing. Storm is simple, can be used with any programming language.

A software versioning and revision control system distributed under an open source license. It is used to maintain current and historical versions of files such as source code, web pages, and documentation.

Apache Tomcat is an open source software implementation of the Java Servlet, JavaServer Pages, Java Expression Language and Java WebSocket technologies. Tomcat implements several Java EE specifications including Java Servlet, JavaServer Pages (JSP), Java EL, and WebSocket, and provides a "pure Java" HTTP web server environment for Java code to run in.

An open source web sever that runs on most UNIX-based operating systems (such as Linux, Solaris, Digital UNIX, and AIX), on other UNIX/POSIX-derived systems (such as Rhapsody, BeOS, and BS2000/OSD), on AmigaOS, and on Windows 2000.   

An open source file API that allows distributed processes in large systems to synchronize with each other so that all clients making requests receive consistent data. It is provided by a cluster of servers to avoid a single point of failure.