Jenkins
Jenkins is a long-standing, open-source automation server for building CI/CD pipelines, self-hosted and highly extensible through a large plugin ecosystem — one of the earliest and most widely deployed CI tools, especially common in established enterprise environments.
Unlike GitHub Actions or GitLab CI, which are built into their respective hosting platforms, Jenkins is a standalone tool a team installs and manages themselves — more setup and maintenance overhead, but also more flexibility to integrate with virtually any source control system, testing tool, or deployment target through its extensive plugin library.
Pipelines are typically defined as code (a Jenkinsfile) using either a declarative or scripted syntax, checked into the same repository as the application — Jenkins remains dominant in many large, established organizations with existing infrastructure investment, even as newer platform-native CI tools have become the default choice for greenfield projects.
