Actually, I am wanting to set up a web-page for such a cooperative
mulitasking via semi-virtual code compiler.  Cooperative multitasking is
very-powerful in an embedded environment where dynamic prioritys and all
the other crap you have under general purpose os is unnecessary.  A
properly constructed piece of software can handle many tasks very quickly,
and remember that on the PIC the interrupt flags are still set regardless
of whether the interrupts for peripherals etc. are enabled, so it is not a
total loss.

My proposed tool would:

1) Be Free, GNU copyleft or the like
2) Start with a simple "compiler" written with GCC, running under
dos/windows/unix, but developed under linux/bsd
3) Expand with a graphical interface, maybe tcl/tk maybe java to describe
the tasks

4) implement both procedural type code, and state machines
5) the user would simply define the processor type and speed, although I
would probably start with the x14 instruction set pic, like 12c671 etc.
because that would keep the cost of trying it out/testing very inexpensive

6) The user would specify the frequency that tasks run and timing etc.
just in seconds/microseconds and the compiler deals with different
clockrates.

7) ideally i see a software where all this could be easily described
graphically, but in a very powerful fashion, almost "like" and HDL for
PICs.

If you are interested in such a project to benefit the entire PIC
community please email me: jamil@scottibox.com