JGraph is a free, mature, and robust Java diagramming library. It contains all the graph visualization, layout, and interaction functionality you might expect in a graph library, including multiple views, layering, zoom, drag and drop, undo, automatic expanding and collapsing, routing, and layouts. You can create workflow editors, BPMN, CAD tools, network diagrams, database visualization tools, and more. It is fully documented, including examples, and has an active support community.
FidoCadJ is a very easy-to-use editor, with a library of electrical symbols and footprints (through hole and SMD). Drawings can be exported in several graphic formats (PDF, EPS, PGF for LaTeX, SVG, PNG, and JPEG). Although very simple and not relying on any netlist concept, FidoCadJ can be considered a basic electronic design automation program. FidoCadJ uses a file format containing only UTF-8 text, which is very compact and suited for copying and pasting with newsgroups and forum messages. This determined its success, as it is quite versatile for simple mechanical drawings as well as for electronics.
UDIG (User-friendly Desktop Internet GIS) is a spatial data viewer and editor with emphasis on the OpenGIS standards for Internet GIS, the Web Map Server and Web Feature Server standards. It provides a common platform for building spatial applications with open source components.
JGraphpad Pro is a complete application framework for rapid development of JGraph tools. It is meant for developers who wish to provide a stand-alone, rich-client graph application. The user interface is configurable with XML, and it uses a plugin architecture for extra functionality. It features a wide range of application components like palette, overview, the ability to export to many image and XML formats, copy and paste, drag and drop, rich text labels, database or backend connectivity, and visual complexity management. You can use it to create workflow editors, call graphs, CAD tools, network diagrams, database visualization tools, and more.
Jmol is a Free, Open Source molecule viewer and editor. It is a collaboratively developed visualization and measurement tool for chemical scientists. Jmol is an active project, and there are new features being added to it on a daily basis. Users are encouraged to modify it to fit their needs and to contribute their changes to the project.