Quaver! With the caveat that you have to map the song yourself, but the game comes bundled with the least painful song map creator tool I've ever used.
IMO, it's better than osu!mania by far in terms of UI and performance. It can also one-click import your song libraries from other games, like o!m and Etterna. I love it, built-in map search too and steam workshop support for skins!