Bemuse comes with a default Official Music Server which contains a collection of 70+ curated songs. There are also Music Servers run by others, which provides access to more contents.
This page attempts to maintain a list of these servers.
the forgetalia
…features 17 songs from the forgetalia project which are geared towards beginners.
METTATUNES
…features 9 songs from the METTATUNES event, a BMS event dedicated to cover/remix/arrangements of songs from UNDERTALE.
TEAM-BMSON
…features 7 songs produced by TEAM-BMSON at the BOFU2016 event.
R.I.P.
…features 3 songs produced by the R.I.P. team at the G2R2018 event.
SHIKI BMS collection
…features songs by SHIKI, hosted by Nekokan_Server.