One of the mods may want to update the news link. The current and correct download loccation is:
ftp://ftp.hyperion-entertainment.biz/AmigaOS4_SDKEvidently there were issues in the way their CMS handled (large) downloads, so it's now available via anonymous FTP.
Also, this SDK is freely available to the public, meaning you do not need to own OS4 or have registered on Hyperion's web site..
