There's also NASLite. This one isn't free, but it's still very affordable with it's $30 price tag. The advantage over FreeNAS is it's better performance (twice the speed is no exception!). On the other side, it does not allow any rights management, which FreeNAS and OpenFiler do.

FreeNAS is based on FreeBSD, while NASLite is based on Linux. OpenFiler is based on CentOS. I haven't tried OpenFiler (yet) myself, but I'm very curious to know how well it works and what it's performance is. It's very hard to find reviews for any of these apps. I've found a few (old ones) for FreeNAS and NASLite, but I've not been able to find any for OpenFiler, which is somewhat surprising.

Oh, and then there's also Open-e. This is a solution not really meant for home use, but they do have a nice trial version which could be used a home since it offers enough for most home users. (biggest downside is storage space is limited to 2TB). Might be worth to try.