I recently had the need to build a virtual appliance, a small Linux server that did one thing, and required no interaction. And by small, I mean really small, tiny. After considering the options and searching around a bit, I found the Tiny Core Linux, and when they say tiny, they mean it. The Tiny Core download is only 12MB.
Tiny Core Linux is meant to be a minimalist desktop operating system. The main download includes a window manager, a text editor, and thats about it. The desktop includes a Mac-like dock at the bottom of the screen, and in the dock is an application to download and install more applications. However, for my purposes, I did not need the GUI, all I needed was a server. So I downloaded and installed the tc-install tool, launched it and installed the OS into a very small virtual machine.
rest here