KMidimon monitors events coming from a MIDI external port or application via the ALSA sequencer, or Standard MIDI Files. It is especially useful if you want to debug MIDI software or your MIDI setup. It features a nice graphical user interface, customizable event filters and sequencer parameters, support for all MIDI messages and some ALSA messages, MIDI playback, and saving the recorded event list to a text file or SMF.
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.
KMetronome is a MIDI metronome with KDE interface, based on the ALSA sequencer. The intended audience is musicians and music students. Like solid, real metronomes it is a tool to keep the rhythm while playing musical instruments. It uses MIDI for sound generation instead of digital audio, allowing low CPU usage, and very accurate timing thanks to the ALSA sequencer.
Mixxx is software for DJs that provides everything needed to create live mixes. It allows you to beatmatch songs and crossfade them together, like you would with turntables and a mixer. It runs without any extra hardware, and offers a wide range of advanced features including comprehensive MIDI controller and vinyl control support. To obtain the lowest latency and highest responsiveness, it uses hardware video acceleration and takes advantage of multi-core CPUs.
KMid2 plays MIDI and karaoke files to hardware MIDI devices or software synthesizers. It supports playlists, MIDI mappers, tempo (speed) control, volume and pitch (transpose) controls, and configurable character encoding, font, and color for lyrics. The graphic views include a rhythm view (visual metronome), a channels window with solo/muting controls and instrument selectors, and a piano player window (pianola).