Is there any legal "compilation CD" for PowerPC Linux or AmigaOS software?
Tons.... Check all the usual Linux suspects (RedHat/Mandrake/Debian/etc) for PowerPC versions of Linux CDs. They are around. There is also YellowDog linux for PowerPC, who also has free download/distribute CDs.
Also tons of free Amiga software CDs. Think Aminet, Fred Fish, old magazine coverdisks, etc. Of course, none of these include the actual AmigaOS or ROM images, as those are proprietary. But plenty of useful software.