That doesn’t make the source code proprietary or non-open, it just means it isn’t a community driven project.

Slackware is still around, no past tense. What makes you think it was closed source?

since it’s JIT, it’s actually faster than Python and Java in most cases.

Java is JIT’d too, and Python can be depending on which runtime you deploy.

What has changed about RPN or calculators in the past year?

Become a Red Hat employee and you get one for free.

(genuinely, I know this sounds like a joke)