Virtual MIDI Piano Keyboard is a MIDI events generator and receiver. It
doesn't produce any sound by itself, but can be used to drive a MIDI
synthesizer (either hardware or software, internal or external). You can
use the computer's keyboard to play MIDI notes, and also the mouse. You can
use the Virtual MIDI Piano Keyboard to display the played MIDI notes from
another instrument or MIDI file player.
Project web site: https://vmpk.sourceforge.io/
Drumstick is a set of MIDI libraries using C++/Qt5 idioms and style.
Includes a C++ wrapper around the ALSA library sequencer interface: ALSA
sequencer provides software support for MIDI technology on Linux. A
complementary library provides classes for processing SMF (Standard MIDI
files: .MID/.KAR), and Cakewalk (.WRK) file formats. A multiplatform
realtime MIDI I/O library and a GUI Widgets libraries are also provided.
Project web site: https://drumstick.sourceforge.io/
License of both projects: GPL v3 or later