1). An OS based on Debian (Debian is based on GNU/Linux)
2). An OS that can run on just about any computer with a CD-ROM drive
3). An OS that can run entirely from a CD
4). An OS that is preferred among those in the GNU/Linux community (up there with Debian, Mandrake, and RedHat)
I just replaced Swiss Cheese XP--Windows XP--with Knoppix 3.2 and I couldn't be happier!