Jatha, a LISP library in Java, is now available from Sourceforge:
http://jatha.sourceforge.net/
http://sourceforge.net/projects/jatha/ (download site)
Yes, there are a dozen of these "tiny LISPs". What distinguishes Jatha?
1) It has been in use since 1997.
2) It has been used to translate the Algernon expert system
shell from LISP to Java, using mostly line-by-line translations.
Hence it is very complete and thoroughly debugged.
3) It implements nearly all of the Common LISP data types, including
packages, bignums and complex numbers.
4) Its DynaType package (org.jatha.dynatype) is a useful library
of LISP data types, even if you don't need a LISP interpreter.
5) It has good integration with Java. Every data type has a toJava()
method, sequences have Iterators, and many of the common predicates
such as numberp() have Java versions, e.g. basic_numberp().
Jatha is governed by the LGPL, which means you can use it in
any system - free or commercial - as long as you contribute any
modifications back to the Jatha project. Full source code is available.
More details are available on the SourceForge web site.