Courtesy of Design and Build Great Web APIs I came across https://www.websequencediagrams.com/

You input a text representation like

home->+WIP: startOnboarding(identifier)
WIP->+customerData: collectCustomerData(identifier, givenName, familyName, email, telephone, text)
customerData-->-WIP: saveToWIP(identifier, givenName, familyName, email, telephone, text)
WIP->+accountData: collectAccountData(identifier, discount, creditLimit)
accountData-->-WIP: saveToWIP(identifier, discount, creditLimit)
WIP->+activityData: collectActivityData(identifier, salesRepId, callDate)
activityData-->-WIP: saveToWIP(identifier, salesRepId, callDate)
WIP->+finalizeWIP: completeOnBoarding(identifier)
finalizeWIP-->-home: goHome
WIP->+cancelWIP: abandonOnBoarding(identifier)
cancelWIP-->-home: goHome

that gets rendered as a sequence diagram.

In many cases that might be good enough to visualize the chatter between processes for a particular scenario.

When needed I use PlantUML and/or GraphViz and generate these diagrams:

• Module dependecy diagram mix xref graph --format dot && dot -Tsvg -O xref_graph.dot
• ERD diagram via pg_graph
• Sequence diagrams for business processes and messaging within application
• Usecase diagrams for business logic on high level
• State diagrams (rarely) when I need FSM

Sequence diagrams were always the most useful of UML diagrams, IMHO. Those apply to message passing between BEAM processes just fine when diagrams are necessary. IIRC there’s even a tool in the core erlang/OTP runtime that will generate them.