Yandex's columnar OLAP database. The fastest open-source analytical DB; powers PostHog, Cloudflare Analytics, Plausible.
From Wikipedia
ClickHouse is an open-source column-oriented DBMS for online analytical processing (OLAP) that allows users to generate analytical reports using SQL queries in real-time. ClickHouse Inc. is headquartered in the San Francisco Bay Area with the subsidiary, ClickHouse B.V., based in Amsterdam, Netherlands.