Hunter Monroe
"Maxima algebraic computation software compiles with ABCL. The test suite runs fairly quickly on Windows XP and, after work by Robert Dodier, 86 percent of the test suite is passed successfully, although some individual tests crash the suite. If you want to compile Maxima with ABCL lisp, check out the Maxima source code and following the instructions in INSTALL.lisp."
Alex Mizhari
I'm using ABCL for various web projects since aproximately 2004. None of them have gone public (so far), so i can't give a link. I released sort of framework for building web apps with ABCL was released into open source: abcl-web. Another thing probably worth mentioning -- bindings to Jena2 RDF/SPARQL library: http://abcl-web.sourceforge.net/rdf.html (it's sort of incomplete but usable, i think).
What i like in ABCL is that it has reasonably stable multithreading, does not crash unpredictably (unlike some other implementations) and can be fixed in more-or-less easy way if something goes bad, and access to Java libs, of course. I had some problems with it, though, to name some: That certainly made experience with ABCL less pleasant that it could be, but in general it was more-or-less good.
Alessio Stalla
I'm currently integrating ABCL in a small, unreleased open source project. It's a sort of graphical object browser for Java (but its GUI sucks badly for now...). It can be run locally or as a client-server application. I'm adding scripting support so you can access some functionality from Lisp (or in principle any other Java Scripting API compatible script engine, though I'm focusing on ABCL).
Ted Kosan
I am in the process of integrating ABCL with MathRider in preparation for when Maxima is able to run on it.