There are various tools that can be used for system design, depending on the specific requirements of the project.

Some commonly used tools include:

UML (Unified Modeling Language): a standardized language for modeling and visualizing software systems, including class diagrams, sequence diagrams, and state diagrams.

ERD (Entity-Relationship Diagram): a diagramming technique for representing the data structures of a system and the relationships between them.

Flowchart: a diagrammatic representation of an algorithm, process, or workflow, often used to visually communicate the logic and flow of a system.

Wireframe: a visual representation of a user interface, showing the layout and functionality of a system without the use of color or graphics.

Whiteboard: A simple but effective way of sketching the ideas and concept of the system, useful for brainstorming and initial design phases.

Tools like Visio, Lucidchart,, Gliffy, Moqups, etc, which provide a user-friendly interface for creating diagrams and flowcharts.

Balsamiq, Axure, Figma, Adobe XD, InVision Studio, etc for prototyping and creating wireframes and mockups.

It's worth noting that the choice of tool depends on the scope and complexity of the project, as well as the preferences and expertise of the designer.