About 2 years ago I purchased a Linux based PDA: the Sharp Zaurus SL-5500. The PDA was intended to be used on Windows and (later) Linux. The initial driver for Windows setup the device as a USB network device, however the latest driver set it up as a normal USB PDA. I found that using the older driver, I can assign an IP address to the device and configure it as a mini server. Although I no longer use it as a PDA, I have set up an Apache Web Server, MySQL database and PHP interpretter on it – all managed by setting up the SSH server. I sometimes plug it on various machines and do some web development or toy around with it.
I only recently heard of the Black Dog pocket Linux server. When plugged into ANY computer it will create a basic X-server and run a few basic (Linux) applications from the device within the host OS (Windows, Linux, etc.). It works similar to the Zaurus’ network capability over USB. Hence it can access anything the host computer can access. Even better it has an intelligent resume feature which can pretty much preserve your working desktop and resume it in place later on a different machine.
It ships with a 400Mhz process, 64MB RAM and base 256MB flash-based storage. My Zaurus, to compare, has 206Mhz, 32MB RAM and 64MB storage. Better yet it comes with a biometric scanner, is only 3.5 by about 2 inches in size, and already comes with Apache, SSH and several other programs ready to run. For about $250 you can get the 512MB model and if you plug in another SD card you can increase your storage easily.
Looks like I just found my Christmas present for myself.