Joplin is free and open source software and you don't need to pay anything to use it. The notes are stored offline on your computer. Joplin Cloud is the paid service that you can use to sync and share notes (but you can sync using other methods too, without paying anything).
This isn't related to the question at hand, but please keep in mind that the next stable version of Joplin isn't going to support Windows versions older than Windows 10. More than that, it's not even going to run on Windows 8.