And somewhat less well known, probably, but cool and potentially useful, nonetheless: ObjectSpace Voyager. It was a framework for mobile code / agents / distributed computing. I tried it out a bit, liked it. ObjectSpace were also the company that came out with JGL - the Java Generics Library, a commercial library for generics in Java, some time before Java itself got generics or even before the Java Collections API came out. I think JGL was inspired by C++'s STL (Standard Template Library).