Qmind is a mind mapping App for OS X which is compatible with FreeMind. Keep in mind that it is not yet complete and in a very rough form. In addition, many things present in FreeMind are not implemented (yet). Thus, make sure to backup your files before opening and editing them with Qmind.
What's new in Qmind
Bug fix: jittering edit box on OS X 10.9 Mavericks
Bug fix: crash when editing in zoomed mindmap on OS X 10.9 Mavericks