Take a look:
- GEF – GUI components for graphical editing, including graphs, (Eclipse) SWT based
- JGraphX – former JGraph, not actively developed since March 2020
- Piccolo2D – (Eclipse) SWT based
- JUNG – last released in 2010 (as of 2020); was very popular back then
- yWorks – not open source, not free
- JGraphT – data handling and algorithms only, no integrated visualizaiton, though supports JGraphX visualization