This article compares FreeNAS with NextentaStor Community. They are both storage operating systems, FreeNAS being based on FreeBSD.
High Level Comparison
FreeNAS and NexentaStor Community are Storage Operating Systems that support many of the same features like CIFS, SMB, NFS, and iSCSI protocols. Each system works with OpenZFS (v5000) with feature flags, most virtualization platforms, and have support, training and certification available.
NexentaStor Community Edition
Alex Aizman and Dmitry Ysupov created the Nexenta OS project after Sun Microsystems released the bulk of its Solaris operating system under free software licenses as OpenSolaris. NexentaStor is derived from the former Nexenta OS and based on the illumos operating system, utilizing OpenZFS as an underlying filesystem. The software delivers unified file and block storage services to consumers. NexentaStor Community edition is free up to 18TB of raw storage and does not include all the features of the professional version.