Some time ago, I bought a LinkSys NSLU2, that's a very cute little box with power, usb and network plugs, and nothing more. Inside sits an ARM processor and 16MB RAM. The great thing is: You can install linux on it, even a complete Debian sarge installation.
The box is not very performant, even after I de-underclocked it by scraping away a resistor from 133MHz to 266Mhz, but it is quite cheap and very handy. I use it for nightly backups. Unfortunately, the attached external Maxtor OneTouch harddrive is quite loud, even when it is idle. Here are the steps I took to make the setup zero-noise as long as the slug is doing nothing:
Set the spin down time for the hard drive using sdparm.
Use noatime on all mounted disks.
Use ext2, not ext3. (maybe that is not necessary, I'll try with ext3 some time)
Run syslogd with "-m 0" to get rid of the 20-minutes "--MARK--" entries. (For debian, set it in /etc/init.d/sysklogd)
Of course, only run stuff you actually need
And the final step, just figured out: Mount /var/run on a tmpfs. Daemons like openvpn seem to write there on regular intervals, so keep these away from the hard drive.
Some further plans for my slug involve a USB attached LCD display and a temperature sensor, so I can be informed about various stuff, incuding the outside temperature, even with my regular computer off. Suggestions of what hardware I could use is highly appreciated.
How about getting the NSLU2 to retreive via the HTTP the weather forecast from the your local weather bureau, and then display a summary of that on your LCD? Then you could have the current weather outside, plus the forecast, without turning your regular computer on.
/dev/sda3 on / type ext3 (rw,noatime)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw)
usbfs on /proc/bus/usb type usbfs (rw)
none on /dev/shm type tmpfs (rw)
none on /var/run type tmpfs (rw,size=512K)
/dev/sda4 on /bigmedia type ext3 (rw,noatime)
/dev/sda1 on /backup/image1 type ext3 (rw,noatime)
/dev/sda6 on /backup/image2 type ext3 (rw,noatime)