ksqlDB

ksqlDB is a database purpose-built for stream processing applications on top of Apache Kafka, letting you write SQL queries directly against Kafka topics — filtering, joining, and aggregating streaming data using familiar SQL syntax instead of writing a Kafka Streams application in Java/Scala.

It turns common stream-processing tasks (real-time aggregations, stream-to-table joins, materialized views over event streams) into declarative SQL statements, lowering the barrier for teams already comfortable with SQL to build real-time data pipelines on Kafka.

Developed by Confluent; used by teams building real-time analytics or event-driven applications on Kafka who want to avoid writing custom stream-processing code for common query patterns.