In-process OLAP database — 'SQLite for analytics'. The most-celebrated dev tool of 2024-2026; runs in browsers, Lambda, Python, R.
From Wikipedia
DuckDB is an open-source column-oriented Relational Database Management System (RDBMS). It is designed to provide high performance on complex queries against large databases in embedded configuration, such as combining tables with hundreds of columns and billions of rows. Unlike other embedded databases DuckDB is not focusing on transactional (OLTP) applications and instead is specialized for online analytical processing (OLAP) workloads. The project has over 6 million downloads per month.