Wikipedia
NASLite is a free commercial Linux distribution designed to turn conventional x86-based computers with PCI interface into a simple network-attached storage device. It fits onto a single 3½-inch High Density floppy disk formatted to 1.72MB. NASLite boots from the floppy disk and runs in a 4MB RAM disk allowing for full capacity of the hard disk drives to be used as storage. NASLite supports serving files to clients running Windows, Linux, Mac OS X as well as others.
Other versions are available which support different networking protocols, or booting the operating system from CD-ROM, USB Mass Storage device or hard disk drive. All versions of NASLite and its variants contain GPL'd and proprietary components. The GPL'd components are available to the end user per the GPLv2.