If you want to access your notes and todo-lists from several computers and your mobile phone then there are several tools you can use. As EasyOrg is based on plain text files there is great flexibility and you do not need to rely on any built in syncing.
One of the most flexible and transparent tools is Syncthing. You can set it up to sync specific files and/or folders and once done they will be kept in sync if you update the files on your computer or on your mobile. Syncthing does not store anything in the cloud.
In this documentation we will not go through how to set it up as it is well explained on Syncthings website.
Other great alternatives are Dropbox, pCloud and iCloud. They make it easy to sync files and folders between several computers and phones. In addition your files get stored in the cloud.
Another great benefit of using text files is that you can get versioning support. You can go back and forth in time to refer to older versions of your Org files. To achieve this you need a solution that provides file versioning. Syncthing, Dropbox and pCloud all support file versioning. Another obvious tool for file versioning is Git.
Thanks to using text files as storage medium it's easy to setup a backup to run every day and store it on another disk or server. You probably already have a backup solution in place and if your Org files are stored within a directory that is backed up, you already have you EasyOrg files backed up!
Other alternatives for sync could be using GitHub, WebDAV, NextCloud, NAS or other cloud storage services.