There's also a number of different open source implementations of various versions of K listed on the K wiki:

https://k.miraheze.org/wiki/Running_K

Thanks, I appreciate the link. As it turns out, it is really hard to google "K"

Yeah. Arthur Whitney's old company is Kx Systems which sells a vector in memory database for things like financial stock ticker analysis called Kdb+. I forget which version of K it is on. It mostly doesn't matter as most folks use the q-sql DSL on top of it. He then started another company called Shakti with some changes and what I guess is a later version of K. He had a download link up for a bit, but took it down iirc. I wish the site had more about the product listed, but we're not exactly the target audience (more for big banks).

Look at one of the captures around the end of 2021.