Use APKPure App
Get Remote osu! Keyboard old version APK for Android
Użyj zdalnego OSU! Klawiatura jako klawiatury do OSU!
Use Remote osu! Keyboard as a keyboard for standard osu!, mania, taiko and catch the beat modes. This makes playing silent and ideal for newcomers to osu.
Before you can start using it, you have to download a server to your computer. You can do so on this forum thread: https://osu.ppy.sh/forum/t/391981.
All you need is a Wi-Fi connection. It doesn't have to be fast, because Remote osu! Keyboard sends as little data as possible across the network.