This is the first release candidate of AntiX, which uses the MEPIS Linux core (which is, in turn, derived from Ubuntu). AntiX sports programs suited for older machines: the Fluxbox and IceWM window managers, AbiWord and Gnumeric for office productivity, Sylpheed-Claws for mail, Firefox 2.x, Pan, Leafpad, the Raggle RSS reader, and a slew of other applications.
AntiX is recommended for machines with 128MB of RAM, but will also work with machines with only 64MB of RAM and 128MB of swap space. MEPIS will run with a minimum of 128MB of RAM, but not very well.
According to the release, the AntiX name derives from the developer's username in the MEPIS forums (anticapitalista) and "it is supposed to be like antics (fun) and antiques (i.e. older boxes)."
While not an official offering from MEPIS, you can grab the testing ISO from the MEPIS mirrors.