An open source modular sound synthesis program being developed by Paul Barton-Davis. It has a very nice looking graphical user interface based on GTK-- and supports the Csound language. It is written using object-oriented design with C++, and is easily extensible.
It is fully controllable from any MIDI device in real-time. It is modelled after hardware modular synthesizers such as the Creamware Pulsar and Nord Modular. At the present development is on hold because the author is working on Ardour, but he has said work will continue on it soon.
It is a very ambitious project, but should be quite revolutionary as, in theory, it will replace gear costing thousands of dollars with free software which will run on a high end computer workstation.