Returning to Cache'

Ive been asked to investigate Intersystems Cache' for a new software initiative and was hoping to be able to download a limited-use or dev license to kick the tires but I need it for a couple of specific OS builds.  AIX and Linux (CENTOS).  I don't see a place to download specific versions, other than Windows, various builds of Unix and that's about it.  Can someone give me some guidance on how to make sure I'm downloading the right item to build some test instances with?  

thank you in advance :)

tom