Diagrams.net
The website diagrams.net is a quite popular online tool for creating simple and non-standardized diagrams.
- π΅ It's free
- π£ It doesn't require much knowledge
- π It doesn't require an account
- π We do not have to install anything
The main disadvantage is that it doesn't enforce a standard (ex: UML).
Without useful and clear explanations (which is usually a complex task), everyone may understand your diagrams in a different way.
It's not appropriate to use this for complex diagrams.