Is there a free version? I was interested I was interested in learning it a few years ago but couldn't find a version that was free for both commercial and non-commercial use, which tempered my enthusiasm.

To my knowledge, there isn't a full OSS implementation of K/Q. I do know of a K5 interpreter in JS [1] but otherwise I've only been able to find the free for personal use 32 bit Q distribution.

[1] https://github.com/JohnEarnest/ok

Kona implements K3 according to its github.

Yeah. It comes bundled with Q in a free non-commercial 32 bit binary. Q and KDB+ is a higher-level 'wrapper' of sorts around the language.

https://kx.com/download/