The barriers to releasing are falling down! g-wrap was released. guile-gnome is about to be released. GStreamer was released a while ago, but it finally works out-of-the-box with soundscrape. I can't be more pleased. Soundscrape will be out by the end of the month.
Soundscrape is a modular software synthesizer with a twist. Unlike in most others, creating the filter flow graph for soundscrape is done via programmatic Scheme code, not boxes and wires. Flexible and brief, soundscrape gives you more expressive power.
Soundscrape is based on Guile, an implementation of Scheme -- a full-power language, not just some funny syntax. When you create your patches in Soundscrape, you have the entire algorithmic power of Scheme at your control.
While the interface to soundscrape is all Scheme, the backend is written in pure C. When the synthesis loop is running, things run fast -- Scheme never sees the data!
James McCartney did an incredible job in the ten years or more he worked on SuperCollider, I'd be a fool not to learn from his work. Unfortunately, I've never actually seen SuperCollider in action, as it only runs on Mac OS 9. Many of SuperCollider's key features can now be found in soundscrape: control and audio rate operation, multichannel propogation, intelligent algorithm choice based on inputs...
Soundscrape is mainly being developed on GNU/Linux, although ensuring that it works on Mac OS X should not be difficult.
Soundscrape conforms to standards set by the Linux audio development community, giving it access to all the plugins you already have on your machine.
Free, with a capital F. You have the freedom to download this software, give it to your friends, and hack on it to your heart's content, subject to the GNU General Public License.
These are all aspects I'd like to have in the "what's cool" category, but for the moment are still a problem. Hopefully over time I'll be moving things from the sucks to the cool category.
The synthesis loop runs in the same thread as the language loop. This makes the interface less responsive as well as making the synthesis less reliable. The cause of this situation is immature threading support in the scheme interpreter, Guile. This problem should be fixed when Guile 1.8 is released.
Although it has been under development for about four years now, GStreamer has not been stress-tested in a realtime environment. GStreamer needs a realtime safety audit. There is, however, nothing that indicates that GStreamer is incapable of realtime operation, provided each element is coded carefully.
Jack is the standard for communication between audio applications on Linux. The threading issues mentioned before are the only thing holding back Jack integration, which is a crucial feature for any Linux audio app.
The equivalent of SuperCollider's "Voicer" element has yet to be written. This should come in time, though.