It's not a big deal by I second that. I also thought, "let's see how they are making money out of this". I clicked on the github link and found out it's GPL 3.0, all of it, no open core or similar stuff.
Maybe a tiny note about it being open source could help.
GPL 3 isn't great for either. From a commercial perspective, you can only use it if you lock your stuff up in a datacenter, but not if you ship it on a device that customers own. In practice, that means GPL 3 is not only supporting surveillance capitalism, but is also banning use in commercial systems that do not spy on their users. (The US CLOUD Act says that you have to provide the government with access to all machines you have access to, even if they are overseas. In practice, that means that any commercial GPL 3 stuff that has a footprint in the US is globally subject to US-style dragnet surveillance.)
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.]
It's taken from "Free as in [Free] Beer vs Free as in [Free] Speech"
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.)
That is the nearest to an explanation in all the answers ie saying "Beer is NOT free' all the others still confuse me as I read its literally. and 'Free as in beer' makes no sense so the whole thing just does not compute.
I do understand what GPL does and the reasons for this just not this slogan.
Maybe a tiny note about it being open source could help.