I have come across the following non-HP sites and they are good places to start when you are looking for more free information about Tandem products.

Please note that everything is provided here on an as-is basis, and the author does not accept any liability, whatsoever. Though your comments may help make things better.

• Wikipedia's Tandem Computers Page
  Very useful and pertinent information about the history of the Tandem Computers,  and heavily cross-linked to lots of relevant information

• Kari Kujansuu's Utilities
  Very useful utilities, written by one of the current HP NonStop employees. Also contains a FAQ on Tandem

• Randall Consulting  -

Home page of a Tandem Consultant. Has some free macros and other stuff which you can use

• Benson Systems

Home page of John Benson, a long time Tandem expert and a consultant. He is also an active and vocal participant at many Tandem related mail groups (like the Tandem_Computers Yahoo Group, which you can subscribe to at the bottom of this page), and ITUG forums

• Rohit Singhvi
   

Some beginner level information about Tandem utilities

• Mark Whitfield

Again a personal website with some historical information about Tandem Computers

• TandemWorld

Good website with some free utilities and a newsletter

• Dennis Adams

Some techical papers, including  Tandem NonStop for Beginners