Yes, it's free, for now...
Sculptris is very cool, a bit glitchy, I can make it crash an awful lot but, very cool, indeed.
I tried the Zbrush trial version before, v3.something, my sweet jeezus, could I figure out the UI? Not in a thousand years! It looks like such a cool app' but I'd need longer than 30 days to work it all out and I don't have the time, or money, for that.