ITS A PRECOMPILED LINUX DISTRO WITH THE TOOLS ALREADY SET UP. For the majority of you this is useless don't even bother to "download for testing" honestly. If you really care that much just get a normal *nix distro and set up all the tools your self. Its really not that hard to get gcc, bison and everything else then download the toolchain and everything needed to compile and develop and do make then write code to compile.
I still need to update my distro(9.10) and re-install the toolchain but I rather just do it on the distro Im already running as to update and install the toolchain is less (like 500mb+700mb) as I already have everything else, plus I still get to keep my current set up and don't have to re-compile my drivers and everything.
I know people who used to make these for the PSP SDK and all those tools and honestly I don't see the point, its just easier to get everything separate that you need. That is unless your a first time linux user and wish to fondle around in PS3 Dev.