I'm trying to catch up on writing posts about some of the open source stuff I've been building out lately. This is an older one, but still useful (I hope) to someone.
mm2tiddlywikitext is a stylesheet that reformats a FreeMind mind map as TiddlyWiki bulleted text. My main use-case for this is importing my mind maps in a searchable way into TiddlyWiki.
The easiest option is to use it directly from within FreeMind. Go to File > Export > Using XSLT.... In the dialog that pops up, provide the path to stylesheet.xslt and an output location. This will create a TiddlyWiki 5 JSON file that can be imported into TiddlyWiki.