The most impressive part of TrueNAS is the barrier to entry. It was incredibly easy to install and configure. Once the initial boot is done, you rarely have to touch the physical hardware again. Everything is handled through the WebGUI, which is clean, intuitive, and surprisingly powerful. Managing disks, pools, and permissions feels modern rather than a chore.

The plugins are great, I host a Plex Media Server on it with my music library that I can listen to while driving places ad free. Also, I have it set up on an old microform desktop computer running a basic file server using the samba protocol that everyone in our family can access from any computer in the house. I've been able to build a few of these for friends as well, and it can work in an Enterprize environment too thanks to Active Directory integration. Really it's an incredible little Operating System that can do so much. It was very easy to install and set to a static IP address, I now run it completely headless and the only interaction I have with it is through the web interface. The UPS it is plugged into failed once, and it suffered from an abrupt power loss... but fortunately the ZFS file system that it uses is built from the ground up to handle things like this and I didn't lose anything even though I was actually streaming video from it the moment that the outage happened!

Many things! ZFS, its management interface, the fact that it has CORE and SCALE. Simple to implement.