What are some alternatives?
When comparing unRAID Server and FreeNAS, you can also consider the following products
OpenMediaVault - OpenMediaVault is the next generation network attached storage (NAS) solution based on Debian Linux.
Rockstor - Rockstor is a free and open source NAS (Network Attached Storage) operating system.
Amahi Home Server - Amahi is a media, home and app server software known for its easy-to-use user interface. Amahi has the best media, backup and web apps for small networks.
Drive Bender - Drive Bender, class leading storage pooling technology
Zentyal - Linux directory, domain, mail, gateway and infrastructure server for SMBs.
StableBit DrivePool - State of the art, file based drive pooling software.