Jenkins

The granddaddy of CI/CD tools. Jenkins has been automating builds since before “DevOps” was a buzzword. It’s open-source, infinitely extensible via plugins, and runs on Java — which means it’ll also eat all your RAM.

Jenkins is like that old reliable truck: it’s not pretty, it makes weird noises, but it gets the job done. Its plugin ecosystem is massive (1,800+ plugins), and its Groovy-based pipeline syntax is… an acquired taste.

Why it matters: Jenkins pioneered CI/CD for the masses. While newer tools like GitHub Actions are shinier, Jenkins still powers a shocking percentage of the world’s build pipelines.