I’m not a mobile platform developer any more but I just wonder: How easy or hard would it be to make a mobile app that syncs all user document files to the other devices on the same account by using something simple as a CRON job that runs RSync every 30 seconds or something in this direction?

I don’t even know if there is a CRON job or equivalent on android or iOS? Or if there is an RSync port for android or iOS. But there should be