Let's make music (LMMS) is a free, cross-platform music app.
"Produce music with your computer
by creating melodies and beats, synthesizing and mixing sounds, arranging samples and much more.
Playback instruments,samples and plugins
with a typing or MIDI keyboard in a user-friendly and modern interface.
Bundled with ready-to-use content
from an assortment of instrument and effect plugins, presets and samples to VST and SoundFont support." - © LMMS