Message Sequence Charts
Swim lane diagrams have been formalized in message sequence charts - what that means.
I was not aware that the ITU had formalized swim lane diagrams into Message Sequence Charts. While you don't need to use these formalizations, the choices they made, and the comparisons to UML's diagrams can be interesting, especially if there are tricky corners where you're having trouble modeling some flow. For example, "They work particularly great in opening up assumptions (e.g., so many times a message from server to another has proven to be actually relayed through a browser redirection) and also if you mark state machine transitions on it, you'll see false assumptions there too."
Thanks to Antti Vähä-Sipilä for pointing them out (along with the use case) in the OWASP Threat Modeling slack channel. (Join via OWASP Slack Channel.)