I'm looking for the program that JSON, SQLite and other projects are using to create the diagrams used for their language syntax, if there is a particular program. All of the diagrams have a similar style, with partially curved connections or arrows indicating flow.
There are some differences, making me wonder if it's a single program or just generic graphing tools used for a particular style.
As you can see by my edits to your question, the kind of syntax diagram you're referring to is also known as a railroad diagram. Wikipedia mentions a few tools under the "External Links" section, including:
See also these related Stack Exchange questions:
Super User: Software to draw/edit the Syntax of SQL statements
Stack Overflow: Tool for generating railroad diagram used on json.org
Stack Overflow: What is a good tool for creating railroad diagrams?
Stack Overflow: What's the name for this type of flowchart?
Stack Overflow: Software for creating “Language Diagrams” structures
Stack Overflow: BNF notation to SVG
