Audio and instrument plugins
I guess I am not the very first one to suggest adding support for audio and software synth plugins. Yet I see in the nightlies new synthisizers. But I wonder what for? There are many plugin available for free in many formats, so IMHO creating you own snyths is a waste of time.
To sum up what everybody knows already here comes a list of plugin formats:
LADSPA, Linux audio plugin
DSSI, Linux software synth plugin
Lv2, Linux audio and software synth plugin
VST/VSTi, cross-platform audio and software synth plugin (for Linux see http://www.linux-vst.com/)
AudioUnit (AU) , OS X audio and software synth plugin
DirectX (DX/DXi), Windows audio and software synth plugin
While besides VST non of them are available on Linux, OS X and Windows each platform has its own goodies. And even better other open-source programs dirtibuted under the GPL have managed to support many of those formats. I refer imn particualr to these:
So, neither the platform issue nor the licensing issue are a reason not add support for these two types of plugins.