Several music creation applications exist which allow a "virtual studio" to be created in a modular way. Software instruments and effects can be placed on screen, and their input and output terminals connected in (nearly) arbitrary configurations. Examples include Buzz, Psycle, EnergyXT, SynthEdit, Reaktor, AudioMulch, Max/MSP, etc etc. Note that few such applications are open source, few are available for Linux, and virtually none can be considered "cross-platform". Nusq will be all three of these.
Nusq is implemented in C++, using the wxWidgets toolkit for its GUI, and will make extensive use of an embedded Python interpreter for various plugins and extensions. Initially Linux and Windows versions will be available, but hopefully ports to Mac and other platforms will appear in due course.
Like most modular sequencers, Nusq relies heavily on plugins. A Python plugin interface will be provided, and recommended for the sake of cross-platform interoperability, although a native interface via compiled dynamically linked libraries is also provided for particularly CPU-intensive or platform-specific plugins. As well as the usual assortment of audio effects and synthesizers, plugins will be used elsewhere wherever possible (e.g. to provide new phrase or sequence editors, live performance interfaces, file importers/exporters, support for new sound drivers, etc). Common existing plugin formats (e.g. VST on Windows, LADSPA on Linux) will be supported where appropriate.
Many modular sequencers completely eschew the more "traditional" user interface seen in commercial DAW applications such as Cubase and Logic (or open-source counterparts Ardour and Rosegarden). While Nusq will inevitably look and feel very different to these applications, it will provide some familiar features such as multitrack audio/MIDI recording (a feature sorely lacking in many of the "pattern-based" sequencers), and the ability to switch between the modular view described in the first paragraph and a more traditional "mixing desk" interface.