AdlMIDI is a command line program that plays MIDI files using software OPL3 emulation (FM synthesis). It has a console UI. It features a built-in selection of 50 patch sets, most of which are General MIDI compatible, but some of which are customized for playing original background music soundtracks of select PC games.
PianoBooster is a program that teaches you how to play the piano as well as the basics of reading musical notation. PianoBooster can play any MIDI files, listens and reacts to what you are playing on a MIDI keyboard. It makes sight reading music fun. It can make use of the "light keyboard" or "guide lamp" feature found in some keyboards, such as Yamaha EZ-200, Casio LK 220, LK-300 TV, and LK-43. Keyboards with this feature can cause specific keys to glow. PianoBooster can use this feature to show beginners which keys to press at any given time, even if they can't read musical notation.
Virtual MIDI Piano Keyboard is a MIDI event 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 or mouse to play MIDI notes. You can use the Virtual MIDI Piano Keyboard to display the played MIDI notes from another instrument or MIDI file player.
ll-plugins is a small collection of LV2 plugins and a host that runs them. All plugins are installed in separate LV2 bundles (except the ones that are closely related, like the math-constant plugins or the mono and stereo versions of the peak meter). The GUIs, for the plugins that have GUIs, are installed in bundles of their own to make it easier for packagers to put them in separate binary packages to avoid Gtk dependencies for the plugins themselves. There are synths, event processors, simple audio and control manipulators and GUI-based plugins.