m3 - Mobile Mind Mapper is a mind mapping program originally intended to be used in web browsers, and thus is compatible with multiple platforms (Windows, macOS, Android, iOS, Linux, etc). That version could read and write moderately complicated Freeplane mind maps, however the architecture wasn't scalable (this was my first app using web technology 😄), and it became clear that the risk of deleting your mind maps (since they reside "within" the web browser) was too great.
A new version of m3 is being developed which will address the above shortcomings and more. The old version will remain available while the new one is being developed, however expect the old one to eventually stop working.
You may want to try out the new version, but keep in mind it's still very much a work-in-progress, things may change (including the file format, which could make your data unretrievable), and will not work offline.