PlantUML is a component that allows to quickly write:

• Sequence diagram,
• Use case diagram,
• Class diagram,
• Activity diagram,
• Component diagram,
• State diagram,
• Object diagram,
• Deployment diagram,
• Timing diagram

And also:

• Activity diagram (legacy syntax)
• Archimate diagram
• Gantt charts
• SALT UI mockups

Furthermore:

• Hyperlinks and tooltips
• Creole: rich text, emoticons, unicode, icons
• OpenIconic icons
• Sprite icons
• AsciiMath mathematical expressions

To know more about PlantUML, please visit http://plantuml.com/