FortuneJack offers 25 free spins just for registration from what I can see on the homepage of the site, and
BitStarz also offers 180 free spins on registration as well. If you're just interested in playing and/or testing out the games on a casino, some casinos allow you to play via play money or tokens like
FortuneJack or
Crypto-Games. Good luck!
As far as I know FortuneJack will require you a little deposit before giving you free spin. I am not sure though. I remember last time I checked it and saw this kind of requirement.