Helm is a free, cross-platform, polyphonic synthesizer that runs on GNU/Linux, Mac, and Windows as a standalone program and as a LV2/VST/AU/AAX plugin.
Lupp
Luppp is a music creation tool, intended for live use. The focus is on real time processing and a fast and intuitive workflow.
Blue
Blue is an open-source, cross-platform desktop application for composing music. Use visual tools together with text and code to create the music of your dreams.
Briar
A framework for audio software development
samplv1
samplv1 is an old-school all-digital polyphonic sampler synthesizer with stereo fx.
Giada
Giada is an open source, minimalistic and hardcore music production tool. Designed for DJs, live performers and electronic musicians.
Pragha
Pragha is a Lightweight Music Player for GNU/Linux, based on Gtk, sqlite, and completely written in C, constructed to be fast, light, and simultaneously tries to be complete without obstructing the daily work. 😉
Persepolis
Persepolis is a download manager & a GUI for Aria2.
Curlew
Curlew is an easy to use, Free and Open-Source Multimedia converter for Linux.
Jitsi Meet
Jitsi Meet is an open-source (Apache) WebRTC JavaScript application that uses Jitsi Videobridge to provide high quality, secure and scalable video conferences. Jitsi Meet in action can be seen at here at the session #482 of the VoIP Users Conference.