The PlantText tool is an online tool for quickly creating UML (Unified Modeling Language) diagrams. Unlike most tools, PlantText can build diagrams without the use of a mouse because it is based on PlantUML markup language.

Gaphor is described as 'WYSIWYG (What You See Is What You Get) UML and SysML modeling environment easy to use that will help you create your applications' and is a Diagram Editor in the development category. There are more than 10 alternatives to Gaphor for a variety of platforms, including Windows, Mac, Web-based, Linux and Android apps. The best Gaphor alternative is Excalidraw, which is both free and Open Source. Other great apps like Gaphor are yEd Graph Editor, Dia, Lucidchart and PlantUML.
The PlantText tool is an online tool for quickly creating UML (Unified Modeling Language) diagrams. Unlike most tools, PlantText can build diagrams without the use of a mouse because it is based on PlantUML markup language.

UMLGraph allows the declarative specification and drawing of UML class and sequence diagrams. The current features are part of an ongoing effort aiming to provide support for all types UML diagrams.

Use simple text to quickly create and share diagrams with your team. Improve your documentation, planning and everyday communication with powerful tools for automatic diagram generation.

These two tools are designed with different purposes in mind: PlantText is for automatic online rendering of text-described schemes, useful i.e. for little schemes inside a web page. Gaphor is an editor with a lot more feature, useful for more complex projects: is WYSIWYG (What You See Is What You Get), handles object shared between multiple diagrams and so on.