Musiclab, including Songmaker (explore sound and layers)

GarageBand: Songwriting app with virtual instruments and sequencer. (Mac devices only)

iMovie: Make music videos. (Mac devices only)

Launchpad: Make and remix electronic music (Mac devices only)

Incredibox: Make loops using sounds generated by voice/beatboxing: Incredibox  (App also available but at a cost)

ChromeLab

Google’s Blob Opera: Manipulate individual blobs to create your own choral composition: Google’s Blob Opera.