In the mind mapping space, the OPML (Outline Processor Markup Language) format is commonly used for document exchange and data interchange. OPML is a standard for representing outlines, and it is well-suited for hierarchical data structures, making it a natural choice for mind map data.

OPML is a simple XML-based format that allows you to represent hierarchical structures, which aligns with the structure of most mind maps. It is used to describe outlines of information, making it easy to export and import mind maps between different mind mapping software and tools.

While JSON is a widely used data interchange format, especially in web applications, it is not as commonly used in the context of mind mapping. OPML has become the de facto standard for exchanging mind map data because it is specifically designed for representing outlines and hierarchical structures.

That said, the adoption of specific formats may vary between different mind mapping software and tools. Some software might support multiple formats, including both OPML and JSON, to provide flexibility in data exchange. However, if you're looking for a format that's commonly used for interoperability in the mind mapping space, OPML is a good choice.

Here's a comparison table of OPML and JSON in the context of data exchange in mind mapping:
| Format | Pros | Cons |
|---------|----------------------------------------------|----------------------------------------------------|
| OPML | - Widely supported by mind mapping tools | - Can be verbose and less human-readable |
| | - Well-suited for representing tree-structured data | |
| | - Established standard for outlining | |
| JSON | - Lightweight and easy to read/write | - Not as widely supported by mind mapping tools |
| | - Flexible and versatile for various data structures | - Not as well-suited for representing tree structures |

Here are some examples of mindmapping applications that support OPML:
* MindManager
* FreeMind
* XMind
* Lucidchart
* Coggle
* MindNode

Here are some examples of mindmapping applications that support JSON:
* TheBrain
* MindMeister
* Ayoa
* Mindly
* iThoughts

In addition to JSON and OPML, there are a number of other document exchange formats that can be used to exchange mind maps. Some of these formats include:
* FreeMind (.mm file extension): FreeMind is an open-source mind mapping software, and you can find information about its file format on the FreeMind website or in its documentation [8].
* XMind (.xmind file extension): XMind is a popular mind mapping software, and information about its file format can be found on the XMind website [9].
* MindNode (.mindnode file extension): MindNode is a mind mapping application for macOS and iOS. You can find information about its file format on the MindNode website [10].
* iMindMap (.imindmap file extension): iMindMap is a mind mapping software developed by ThinkBuzan. Information about its file format can be found on the iMindMap website [11].