lyb!mania 4key 2nd is a free multimedia application available on the Android platform. It is a simple reimplementation of mania with some new features. The program only accepts osu!mania format with 4 key amounts.

Despite its buggy state, lyb!mania 4key 2nd offers some new features compared to the lyb!mania v1. The app now allows for holding notes, landscape mode, and hitsounds. The interface is simple and easy to use, making it accessible to both new and experienced users.

However, it is important to note that lyb!mania 4key 2nd is not affiliated with Osu Ppy Ltd and is a separate entity. If you encounter any bugs or crashes while using the app, you can report them through the developer's GitHub or Discord page.

Overall, if you are looking for a simple mania reimplementation with some new features, lyb!mania 4key 2nd is worth trying out. Just keep in mind that it is currently in a buggy state.