BeanShell is a very cool Java application that basically provides a loosely-typed shell environment based on Java syntax. The shell has access to all the classes that are found in its classpath. All I've done so far is play with it a little, but the author, Pat Niemeyer, has put in so many options for running the interpreter (embedded, as a servlet, etc.) that it's a bit mind-boggling. I highly recommend that Java and/or scripting geeks check it out.