Jenkins is a popular open-source automation server written in Java. We can automate anything with it using plugins.
Woodpecker is a simple CI engine with extensibility. It focuses on executing pipelines inside containers.
Drone is a self-service Continuous Integration platform for busy development teams
Git with a cup of tea. Gitea is a painless self-hosted git service. Gitea is a community managed lightweight code hosting solution written in Go. It is published under the MIT license.