One caveat...if you get the free Kontakt Player and then download some free sound libraries, read the fine print carefully, as a number of libraries actually require the full Kontakt product and won't run in the free player.
Indeed... it's free and so are the sound libraries but yes, they do limit the sounds you can play. However, there are often a sufficient number that work to do quite a bit of playing around and writing.
I've said it before about the free demo's for melodyne and Ozone as well as NI.... be prepared to buy the full version since in most cases, you will love it and want the full working versions of those things.