I've been running this Linux distro in a VM, and it's pretty damn impressive, and ultra light. It's Debian stable based, and comes with either Plasma or Trinity as the DE. And check out the requirements:
Plasma desktop - 1GHz CPU / 1GB RAM / 5GB disk
Trinity desktop - 300MHz CPU / 128MB RAM / 3GB disk
I searched the forum and couldn't find even one post about it, so I just wanted to spread the word. It's currently only available on x86 and ARM, but I think a non-official PowerPC build would be pretty amazing if that ever happens.
q4os.org
A good overview of it:
Plasma desktop - 1GHz CPU / 1GB RAM / 5GB disk
Trinity desktop - 300MHz CPU / 128MB RAM / 3GB disk
I searched the forum and couldn't find even one post about it, so I just wanted to spread the word. It's currently only available on x86 and ARM, but I think a non-official PowerPC build would be pretty amazing if that ever happens.
Q4OS - desktop operating system

A good overview of it: