It seems odd to me not to mention things like MaxMSP or PD in an article like this. Arguably Max is one of the most successful standalone visual programming languages (standalone in so far as itβs not attached to a game engine or similar - it exists only for its own existence).
Sometimes the flowgraph is too complex to be constructed using the visual editor though, for example gnss-sdr uses C++ to generate the GNU Radio flowgraph: https://gnss-sdr.org/docs/control-plane/
No, they are very tailored to that use case. They arent general languages - but they are still probably the best examples of successful visual programming languages.