Dear friends:

Thanks a lot for all your precious information. So we can basically say that all other fluids (except brake fluid) cannot be used in a brake system because of the following main reasons (which other fluids do not have):

1) brake fluid is very incompressible (for braking purpose)
2) brake fluid has high boiling point (for safety purpose)
3) brake fluid has very low freezing point (for very cold environments)
4) brake fluid is not corrosive with brake seals (for longevity purpose)

Eric