ZMind is a mind mapping app compatible with FreeMind (*.mm) files. Suitable for small devices since it can display the mind map as a both a list and a tree.

To open a mindmap use the built-in file browser (ANdroid 4.4+) or locate it on your phone by using Google drive, Dropbox, a file browser or something similar. Then clicking on the file will open it with the viewer. You can also create new file locally on your device.