You can theoretically build FractalNow from sources for any Posix-y platform, provided Pthread, GMP, MPFR, MPC and Qt libraries are available for it.
Builds for 32-bit ans 64-bit Windows are available directly on this page, as well as Debian GNU/Linux packages for i386, amd64 and armel architectures.
As for MacOS builds, RPM packages, and others, your help is needed.
Latest release (0.8.1)
Debian GNU/Linux packages
All previous releases are available on SourceForge.