An SMMSTORE file is a collection of local mind maps created by the macOS (OS X) version of SimpleMind, a mind mapping tool used to brainstorm and organize ideas. It contains a local mind map store, which is a directory that stores all of your local mind maps and related information. SMMSTORE files are used for backing up local mind maps, moving between different editions of SimpleMind, and moving them to a different computer.

The SMMSTORE file can only be opened in the macOS version of SimpleMind. If you come across the file in Windows you will not be able to open it. You can import it in the macOS version of SimpleMind (except for the free edition) by selecting MindMap → Import Mind Map Store.... You can also import an SMMSTORE file by selecting SimpleMind → Preferences... then choosing "Local Mind Maps" and clicking Import Mind Map Store.