The MUSCLE system is a fast, portable, flexible client-server system for distributed applications. Clients send BMessage-like PortableMessages to each other either directly or via a centralized server (with built-in database and 'live query' support).
BIM is a Java based AOL Instant Messenger (AIM) Client featuring a full feature Swing GUI. BIM also comes with encryption support. It has a small code base (617KB w/encryption libs) and can be easily dropped and run on wide array of operating systems.