kcr pointed me at
Martian Technology last night over dinner. They seem to have one product; it's an x86-based silent bookcase fileserver ("about the size of a ream of copy paper"), with a 120 GB disk, 100base-T Ethernet, and 802.11b wireless. It's almost the right thing, if it had a second Ethernet port; I could use it to replace donut, which is perhaps a little loud and definitely getting old. Maybe a little on the expensive side.
no subject
The 802.11b is a PCI card - you could certainly get one of the non-wireless units and put another $5 ethernet card in instead, assuming that the riser is still included.