Puppy Linux is a longstanding ultra-lightweight distro. Dog Linux is an example of what happens when a Puppy grows up, becoming stronger, but still lightweight. There are two Dog Linux variants. One is based on Debian, but this is the one based on Ubuntu, Xenial Xerus. XenialDog has a persistent save option – if you have a partition with a label of casper-rw, or a file called casper-rw in the root of a hard disk partition, any changes will be saved there.
Login details: username & password puppy