Apache Hadoop
Open source framework for distributed storage + compute on commodity hardware. Doug Cutting, Yahoo, 2006. Based on Google's GFS + MapReduce papers.
Components: HDFS (file system), YARN (resource manager), MapReduce (compute model). Created the entire "big data" era 2008–2015. Cloudera, Hortonworks (merged 2019), MapR were the big commercializers. Has fallen out of favor with cloud-native data (Spark directly, lakehouse architecture, Snowflake/BigQuery). Still alive in on-prem large enterprises and bank/financial institutions.