A few years ago, I decided to build myself a fileserver. Based on my criteria (free software, extensible, parity-based redundancy), a custom-built system was the best option; and for an operating system, I settled on FreeNAS. It let me get features I wanted (basically the entire ZFS featureset) without jumping headfirst into administering a BSD system, something I'd never done at the time. And it worked very well; installation is as simple as flashing an image onto a USB thumb drive, booting the system off that thumb drive, and setting things up through the surprisingly usable web interface. (I have a general antipathy to web anything as bad technology used by bad people for bad things. But the FreeNAS folks, as of version 8.3 anyway, kept their pants on about it and so, at the client end, it's solidly simple and usable.)