Under Files link are present these folders:
release - contains the latest version of the SPL framework. There is an archive with the name of the current version and spl-latest.zip which is the copy of the latest version but with fixed name. It allows to have fixed link to the current version.
SupportFiles - contains old versions of the SPL Eclipse plugin update sites.
eclipseupdatesite - there is the update site of the current version of the SPL Eclipse plugin.
HudsonPlugin - current and older SPL Hudson Plugin revisions are present in this folder
documentation - user manual and development documentation is present here. It is a good place where to start exploring the SPL tools functionality.