Cat has potential applications in many domains. I can envision a place for it in embedded devices due to its compact and expressive nature. I also believe that Cat would be useful in a computer-science curriculum as a tool for explaining the rudiments of computer programs. The immediate feedback you get viewing the stack after each instruction can be useful for instruction. My intentions are to use Cat as an intermediate language for translation and optimization for my other computer language projects, and as a language for teaching programming.
If you are interested stack languages and aren't familiar with Forth, a fun primer is a fully documented bootstrapping compiler by Richard W.M. Jones (www.annexia.org/forth). I also recommend Manfred von Thun's writings on Joy, even if you never plan on using stack languages. Some up-and-coming stack languages are Factor (www.factorcode.org) by Slava Pestov and Ripple (ripple.fortytwo.net) by Joshua Shinavier, a stack language designed for the Semantic Web.
Thanks to the members of the concatenative mailing list (tech.groups.yahoo.com/group/concatenative), the Cat mailing list (groups.google.com/group/catlanguage), and the Lambda-the-Ultimate.org programming language blog. In particular, I want to thank William Tanksley, Joshua Shinavier, Frank Krueger, and John Nowak.