[BMarkmann]

If you mean "free" as in open-source/free, there is J, which has its own builtin database. I'm assuming it's similar to k/kdb, but that's just a guess.

Learning an APL variant... not a free lunch. Takes a while and commitment to grasp.

[jodrellblank]

J language is free, J database isn't - "Jd is a commercial database product from Jsoftware" - https://code.jsoftware.com/wiki/Jd/Overview

[7thaccount]

I've played with J and read a book on it. It's expressive and powerful of course, but wasn't nearly as natural to me as APL or Kdb+.