strangefx
StrangeFX is a Java(FX) based Quantum computer visual editor. It leverages the Quantum computer simulator software exported by the Strange project. Have a look at Strange to get started with the concepts. The samples at QuantumJava leverage Strange and StrangeFX to visualise circuits that are created programmatically.
StrangeFX also has a UI editor that allows users to create quantum circuits with a drag and drop interface. This editor is undergoing a major refactory, and will be available in Q1 2021.