Cursynth is described as a graphical, polymorphic music synthesizer that can operate via a computer keyboard or MIDI keyboard. Cursynth features two oscillators with 15 anti-aliased waveforms, 32 voice polyphony, filters, and a routable modulation matrix.
Before getting too excited over GNU Cursynth, it's the projects first official release and likely won't take on professional audio creation anytime soon... The GUI for Cursynth is written in ncurses and from the terminal. This GNU musical program is licensed under the GPLv3 and reportedly works on both Mac OS X and Linux.
For more details on GNU Cursynth that saw its first official release (v1.4) this morning, visit its GNU.org project site.