How to set own file file type

I want to set my desktop app file set .note for all OS - windows, mac, Linux. How can I do that?

at windows it could do the installer, as example innosetup can do this.
or you need to add this file extenstion to registry.

i guess you will open the app which belongs to the extention.

Have you read this page ?

http://documentation.xojo.com/getting_started/using_the_ide/file_type_group_editor.html