LMMS lets you sequence, compose, mix and automate songs in one interface, play notes with a MIDI keyboard or your computer keyboard, and use its 16 built-in synthesizers, SoundFonts, VST instruments and effects such as compressors, EQ and reverb.

Download it from lmms.io for Windows, macOS or Linux and install it – no account is needed.

LMMS describes itself as a 100% free, open-source, community-driven project. There is no paid version.