NAS4Free is the original freenas code, which went into a bit of a neglect phase. There was also talk of rewriting on Linux before the fork, which triggered the FreeNAS fork I believe.
On Nas4free jails are still unsupported. You can have them, but you'll be doing so via terminal. FreeNAS has them in the GUI, and it's standard for plugins to run in a jail.
I stopped following nas4free too closely when I went with the freenas side, so there may be other differences. I haven't used nas4free since it was still freenas, so it's not fair to give detail differences.
On Nas4free jails are still unsupported. You can have them, but you'll be doing so via terminal. FreeNAS has them in the GUI, and it's standard for plugins to run in a jail.
I stopped following nas4free too closely when I went with the freenas side, so there may be other differences. I haven't used nas4free since it was still freenas, so it's not fair to give detail differences.