steamclienthomebrew/millennium

Millennium is an open-source tool that lets you install themes and plugins on the Steam desktop client, the app gamers use to buy and launch PC games. Without something like this, Steam's appearance and behavior are fixed. Millennium acts as a framework that sits alongside Steam and injects custom styling and code, letting users change how Steam looks or add new features without modifying Steam's own files directly. For themes, Millennium loads custom CSS and JavaScript into specific Steam windows. This means you can apply a dark skin, change fonts, recolor elements, or swap the entire visual style of the client. Theme authors can also expose adjustable options so users can tweak colors or toggle features without writing any code themselves. For plugins, the framework provides two containers: one running in the Steam browser interface using TypeScript and React, and one running in the background using Lua. Plugins can intercept and modify network requests Steam makes, inject code into Steam's built-in browser, and call between the two containers. This allows for more involved modifications, such as adding new panels or altering how Steam fetches data. A curated plugin database is maintained separately by the project team. Plugins listed there have been reviewed and are tested against current Millennium releases so that they do not break when the framework updates. Millennium runs on Windows, Linux, and macOS. The macOS version is described as experimental. Installation follows a short guided process described in the project's documentation site. Developers who want to create their own themes or plugins can follow templates and documentation the team has published. Adding a new language to the Millennium interface is also possible by contributing a translation file based on the existing English locale.