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. It works in Windows, macOS and Linux.
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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 for Linux, Windows, and Mac OSX.
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License of both projects: GPL v3 or later