This thing is one of the be-all-end-all solutions to people wanting to access their multimedia files around their house, but it runs Windows Home Server. Is there any similar device out there running Ubuntu Server, some variation on Ubuntu, or a version of Linux at the very least?
The whole idea behind the Windows based media centres that are out there is that you spend as little time as possible configuring them (in theory, if you have a Windows home, they should just work). An Ubuntu (Linux) based alternative should have the same sort of 'take it out of the box and start playing' setup.
What are my options?
Assuming you are talking about a piece of hardware you can buy, I'm afraid there is nothing out there (to my knowledge).
The Boxee Box does run on top of a Linux operating system, but I don't think that meets your needs. (And the underlying Linux isn't easy to get to/obvious it's there, in the same way Windows Home Server is on the system you linked to.)
However there are a number of 'Media Centre' software packages that run on top of Linux and Ubuntu that you can manually install: examples include MythTV (see also Mythbuntu), Moovida and LinuxMCE. Again though, I'm not sure if any of these directly meet your needs.
In this kind of installation, you need, at least, 2 things :
Communication protocol between server and client is important and there is an open standard called UPnP that does a good job and works with a lot of different clients. There are other (ie Airplay system in the Apple world) that i do not know.
UPnP Server can stream Videos, Pictures or Audio
So if you run an UPnP media server, you'll be able to :
Most of recent NAS Systems offer UPnP server feature (and others like download station, backup, ...), mine is a Synology and is based on Linux. I can connect to it using telnet or ssh, it's not ubuntu but its a Linux.
My NAS contain all my files and I can access them from everywhere (my home network and even from Internet) using any compatible device.
Hope this help.
My solution doesn't run Ubuntu, and I'm not sure if there is any off-the-shelf solution that does, but it is open-source.
In my mind, the best solution would be to combine the Boxee Box with a separate storage solution (Some sort of NAS device, such as this. The Boxee Box doesn't contain any internal storage media, so you have to supply your own. It does however support the playing of pretty much any media format under the sun, so there's no need to spend hours, or even days, converting large numbers of video files.
The other great thing about the Boxee Box is that it provides a TV oriented interface for accessing media sources in the cloud, through a wide range of native apps. It also comes with a remote that on one side has a couple of navigation buttons, but when you flip it over you end up with a full qwerty keyboard for typing.
The DLink DNS-323 is linux and has MediaTomb as a media server but the 500mhz processor on the device is a little too weak to really handle a drive full of files that is larger than about 250mb.