Graphviz has saved my bacon so many times throughout my career. Not just for visualising constraints and dependencies in planning and scheduling (construction, not computing) but in so many other areas.
Best example was for fabrication of a large subsea structure. Often, these critical assets have material traceability requirements on-par with space exploration, producing thousands of pages of certificates and documentation along the way.
I.e. you need to prove and assure the provenance of every piece of material sitting on the 1km down on the ocean floor back to the assay report of the soup in the ladle at the forge when it was formed, and everything in between; material certificates, design specs, third party testing, mother plate to material stock to final cut part identification, and all the third-party witnessing and assurance along the way. Easy for small parts but cumbersome for 60tn structures with thousands of parts and welds.
When the requirement is 100% QA/QC coverage, linking IDs to certificates and other documents in each part of the chain meant we could easily visualise things and look for rogue elements like child parts pertaining to be from two seperate mother plates, or destructive testing coverage for all materials.
Not how it's usually done but it was a useful tool for communicating to other not so technical stakeholders and helping some on the project sleep easier. :-)