I recently tightened up the well regarded Salamander Piano sampled by Alexander HolmFeel to hopefully make it a bit more responsive. The page also has the piano sampled for the OLPC project by Dr. Mikhail Krishtal. Both are Creative Commons Attribution. Hopefully you guys don't mind me mentioning them.

http://bestofbigcat.blogspot.com/2016/04/salamander-and-summer-pianos-yamaha.html

Do these require "full" Kontakt? Or will they work with the free Kontakt player?

Thanks.

Salamander piano is also available in SFZ format, then you can use it with sforzando which is free.

Sorry it requires the full version, as Fredric L notes it works great with Sforzando. You can get it here though it requires some decompression.
http://freepats.zenvoid.org/Piano/

Even the full version is not good enough!

I have Kontakt v5.4.2.245
The two pianos is question won't work with it.

NI is in the habit of forcing us to upgrade every time a new library comes out.