Open Cubic Player A music file player for Linux, Unix, DOS and Windows 95-ME, XP.

ocenaudio is a cross-platform, easy to use, fast and functional audio editor. Audacity is free, open source, cross-platform software for recording and editing sounds.

MIDI Software for Linux

Midish is an open-source MIDI sequencer/filter for Unix-like operating systems (developped and tested on OpenBSD and Linux). Implemented as a simple command-line interpreter (like a shell) it's intended to be lightweight, fast and reliable for real-time performance. Midish is open-source software distributed under a BSD-style license.

XPMIDI a graphical frontend to the aplaymidi or pmidi program.
GitHub - sobataro/xpmidi-plus An improved version of Xpmidi.
GitHub - mattncsu/xpmidi-plus fork of sobataro/xpmidi-plus with one extra fix.

Eplaymidi MIDI player, MIDI status display, MIDI file selector and WRD player for Open Sound System (OSS).

Widi Midi Players for Advanced Linux Sound Architecture/Open Sound System.

Widi Web + MIDI devices, made easier. GitHub - davemackintosh/widi Distributed under the MIT license.