yEd is a free tool for creating diagrams.
yEd’s positive features:
- automatic layout
- UML diagrams
- BPMN diagrams
- Entity Relationship diagrams
yEd comes with many examples (see help->Example graphs). One can also import shapes and symbols.
- Diagramming software
- Network diagram software
- Unified Modeling Language tools
- Business Process Modeling Notation tools
Xmind is an alternative, especially for brainstorming.