Jenkins is an open-source automation server, used mainly for continuous integration and continuous delivery (CI/CD). It is a self-contained, Java-based program configured through a web interface, and it can distribute builds, tests and deployments across several machines. Hundreds of plugins in its Update Center connect Jenkins to most tools in a CI/CD toolchain. It can be installed on Windows, Linux and macOS, in Docker or Kubernetes, or by running the WAR file directly.
Jenkins is a community-driven project within the Continuous Delivery Foundation, and Linux Foundation legal entities hold the project's assets. The core is licensed under the MIT License, and plugins must use an OSI-approved or public-domain-equivalent licence. The project does not operate a hosted service itself: organisations run Jenkins on their own infrastructure and so decide where builds and data are located, for example within the EU. Plugins are separate community projects, and the ones you choose shape your dependencies.