From the publisher's website:

The GURPS Infinite Worlds setting has its share of strange worlds. But what if the world next door doesn't resemble an alternate history or a strange science-fiction story, but rather a four-color comic book?!

GURPS Infinite Worlds: I.S.T. provides brief information on how to incorporate the GURPS International Super Teams setting into your Infinite Worlds campaign. It's not a stand-alone product -- you'll definitely want the International Super Teams book to use this information fully. But it provides a taste of that world if you're not familiar, and a useful means of integrating it into the Infinite Worlds setting if you are!