the Future of the Theory, And The Generation of a Living World by Christopher Alexander presentation recorded live in San Jose, California, October, at The 1996 ACM Conference on Object-Oriented Programs, Systems, Languages and Applications (OOPSLA).
Guy Steele's keynote at the 1998 ACM OOPSLA conference on "Growing a Language" (mostly about JAVA) discusses the importance of and issues associated with designing a programming language that can be grown by its users.