Another option is to write an LMMS plugin for Csound. That would mean developing a Csound plugin for LMMS that implements the LMMS Instrument.h interface. I have never tried this, so I don’t know how hard that is. The required tools are a C++ compiler, the version of the Qt SDK that LMMS uses, and of course the Csound library and header file.
I glanced at the sources, and it seems not exactly beginner level, but not too bad. I’d start with some existing LMMS plugin, copy it, pull out the guts, and replace them with Csound.
Okay, yes, I am on Linux – and now have Michael’s download, thanks!
And Cabbage… was impressive when I tried it; but was still crashing a lot back then. Another possibility, though I was mainly wanting to throw in diskin for live audio.