MediaTomb is an open source (GPL) UPnP MediaServer with a nice web user interface, it allows you to stream your digital media through your home network and listen to/watch it on a variety of UPnP compatible devices.
Grml is a bootable live system (Live-CD) based on Debian. Grml includes a collection of GNU/Linux software especially for system administrators and users of texttools. Grml provides automatic hardware detection. You can use Grml (for example) as a rescue system, for analyzing systems/networks or as a working environment. It is not necessary to install anything to a harddisk; you don't even need a harddisk to run it.