IBM's proprietary Unix [L1 ]. For branding purposes, the company tries to talk about the "eServer pSeries".
AIX FAQs [L2 ]
Recently on comp.lang.tcl someone mentioned:
You can get Expect, Tk, and TCL direct from IBM.
http://www-1.ibm.com/servers/aix/products/aixos/linux/altlic.html
One thing that would be appropriate for this page is tips on how to get Tcl and associated extensions to compile on AIX.