IMSLP
imslp.org
Free scanned sheet music for almost the entire classical repertoire
flat.io
Write and hear proper sheet music in a browser, with real-time collaboration.
A notation editor that behaves like a document: multiple people can edit the same score at once, it plays back with reasonable instrument samples, and it imports and exports MusicXML and MIDI so scores move to and from desktop notation software. MIDI keyboard input works in the browser. It is the realistic free option for arranging a part or writing a lead sheet without buying Sibelius or Dorico.
Questions
A genuinely usable free tier with paid plans for volume or team features. The free plan stops at fifteen scores and thirty instruments, and clean unbranded exports need the paid tier.
Yes. Flat sends your input to its own servers to process it. That is fine for public material; for anything containing personal data, use one of the on-device tools instead.
The free plan stops at fifteen scores and thirty instruments, and clean unbranded exports need the paid tier.
Alternatives
Same category or same task, ordered by how closely they overlap.
imslp.org
Free scanned sheet music for almost the entire classical repertoire
bandcamp.com
Stream independent music in full, and buy it as lossless files if you want it
musiclab.chromeexperiments.com
Fourteen small experiments that let you build a rhythm and see harmony move
freesound.org
Half a million Creative Commons sound samples, searchable by how they sound
metronomeonline.com
A metronome that starts clicking the moment the page loads
music-map.com
Type one band and get a cloud of the artists people who like them also like