extensible

Jenkins is the leading open-source automation server that enables developers to build, test, and deploy their software. With over 1,800 plugins and a massive community, it provides unparalleled flexibility and extensibility for continuous integration and continuous delivery workflows.

GitBucket is a Git platform powered by Scala with easy installation, high extensibility, and GitHub API compatibility. It provides a GitHub-like experience for self-hosted Git repositories with a focus on simplicity and compatibility.

Mopidy is an extensible music server that offers a superset of the MPD API, as well as integration with 3rd party services like Spotify, SoundCloud etc. Built with Python, it provides a flexible platform for music streaming with extensive plugin support.

Buildbot is a continuous integration framework based on Python that automates the compile/test cycle required by most software projects. It provides a flexible, extensible platform for automating software builds, tests, and releases with support for distributed builds across multiple platforms.

Serendipity (s9y) is a highly extensible and customizable PHP blog engine using Smarty templating. Built with PHP, it provides a flexible, plugin-rich blogging platform with advanced customization capabilities and a strong focus on extensibility and developer features.