DJ
Support for adaptive programming (dynamic structure-shy traversals and visitors) in pure Java.

HyperJ [IBM]
A Java tool supporting advanced Multi-Dimensional Separation of Concerns. [Freeware]

Aspect Browser
A tool for Java (with optional Emacs support) which helps developers to find and visualise crosscutting concerns, using text matching. [Freeware]

Specialisation Classes
Specialization classes are a Java language extension for integrating forms of adaptive behavior in an existing program. An adaptive class is defined by attaching a number of alternative implementations to a regular Java class, that complement the existing, default implementation. [Freeware]

DemeterJ
An adaptive programming language based on Java. The "big sister" of DJ.

Sally
A general-purpose aspect language (GPAL) based on Java, with aspect reflection.

Concerning AOP and Inheritance
Paper in PDF format which introduces the Java-based language Sally and compares it with AspectJ: interactions as opposed to method entry, named advices, advice overriding. Also compares aspects, conventional inheritance, and mixins.

JAC (Java Aspect Components)
Aspect-oriented application server and development environment. [Open Source, LGPL]

Macker
Helps enforce architectural rules (layering, tiering, and modularity) in Java code. It applies pattern-based access rules from XML rules files to compiled classes. [Open source, GPL]

AspectJ
Aspect-oriented Java extension, seamless, from Xerox PARC. Goal: to make aspect-oriented programming (AOP) technology available to a wide range of programmers. [Open Source, MPL]

EAOP tool
A research prototype for Event-based Aspect-Oriented Programming (EAOP) for Java.

AspectJ, 0.8b5: Real-world AOP tool simplifies OO development
Detailed review of the aspect-oriented Java extension AspectJ 0.8, by Rich Price, a senior staff engineer at CheckFree Corp.

abc: the AspectBench Compiler for AspectJ
The distribution of an optimising, extensible compiler for AspectJ, freely available under the LGPL. The abc project is a joint effort between the University of Oxford (UK), McGill University (Canada), and the University of Aarhus (Denmark). [Open source, LGPL]