Puppy:

Yes, Puppy Linux is yet another Linux distribution. What's different here is that Puppy is extraordinarily small, yet quite full featured. Puppy boots into a 64MB ramdisk, and that's it, the whole caboodle runs in RAM. Unlike live CD distributions that have to keep pulling stuff off the CD, Puppy in its entirety loads into RAM. This means that all applications start in the blink of an eye and respond to user input instantly. Puppy Linux has the ability to boot off a flash card or any USB memory device (flash-Puppy), CDROM (live-Puppy), Zip disk or LS/120/240 Superdisk (zippy-Puppy), floppy disks (floppy-Puppy), internal hard drive (hard-Puppy).

Slax:

Imagine the ability to boot your favorite Linux distribution whether you are at home, at school, or at work. Imagine walking on the street and carrying the only thing you needed in life. SLAX is fast and beautiful Linux operating system that fits this description. It is based on Slackware Linux and uses the KDE desktop.

Ubuntu:

Ubuntu is a complete desktop Linux operating system, freely available with both community and professional support. The Ubuntu community is built on the ideas enshrined in the Ubuntu Manifesto: that software should be available free of charge, that software tools should be usable by people in their local language and despite any disabilities, and that people should have the freedom to customise and alter their software in whatever way they see fit. "Ubuntu" is an ancient African word, meaning "humanity to others". The Ubuntu distribution brings the spirit of Ubuntu to the software world.