tl;dr: ClickHouse, released as open source on June 15, 2016, grew out of creator Alexey Milovidov's prototypes (OLAPServer and Metrage) built at Yandex starting in 2008-2009 to handle web analytics workloads that existing databases couldn't manage. Unlike most modern databases built atop Postgres, DataFusion, or others, ClickHouse was written entirely from scratch, evolving through column storage, aggregate functions, MergeTree, and ZooKeeper-based replication before its public release. Ten years on, it has 2,000+ contributors and is one of the most popular open-source analytical databases.