Software to start creating virtual instruments

A few weeks ago I started to dive into creation of “digital” instruments to use them in any DAW (Cubase, in my case), or even as playback sound font for MuseScore, for example. I got quite disappointed. I did not find what I was searching for. There is Steinberg’s HALion (expensive, really complex) and Native Instruments' Kontakt (even more expensive), and EXS24 for Logic Pro But with neither of them it is possible to create or export instruments in a format which can be distributed for free so that it can be used by others without a Cubase, Logic or Kontakt license.