Maybe a tiny note about it being open source could help.
Gmail is free as in beer, but not free as in freedom, while RHEL is free as in freedom, but not free as in beer.
Gratis vs Libre - the former is zero cost (i.e., you're not paying for the free beer), the latter is some cost (i.e., there is a price for free speech - we need to defend the right, accept we won't like everything that is said, etc.)
I do understand what GPL does and the reasons for this just not this slogan.
Granted, bash is now GPL 3 (which is why Apple has to ship an obsolete version, and now defaults to zsh), so you can't use Amber on machines where GPL 3 won't fly (unless it can also compile to posix shell, zsh, etc).
Anyway, if you're interested in freedom for your users, I'd suggest AGPL 3, since it prevents people from locking it up inside the cloud or shipping with proprietary operating systems. At least that way, you're not stripping users' right to privacy like GPL 3 (inadvertently?) does.
These days, Apache and BSD-style licenses are looking better than ever to me, at least when I'm at work.
[edit: You can sell machines with Coreboot (and maybe a proprietary BIOS) + bash. However, you can't ship things that use a secure boot mechanism.
From reading the FSF documentation, it's not clear to me if it's OK to ship a GPL 3 userland on a machine with secure boot enabled, even if it can be disabled later. Apple apparently decided that it is not.]