It's written in Qt.
Features:
- Adjustable grid
- Automatic layout optimization
- Easy-to-use UI
- Export to PNG or SVG
- Forever 100% free
- Full undo/redo
- Nice animations
- Quickly add node text and edge labels
- Save/load in XML-based .ALZ-files
- Translations in English (default), Finnish, French, Italian, Dutch
- Very fast
- Zoom in/out/fit
- Zoom with mouse wheel