Simple Journal is a simple Windows application that allows you to create a locally stored journal. The file format is simple -- RTF files stored within an encrypted zip files -- so you do not need the client installed to be able to read or write entries.
For more information on the motivation behind Simple Journal, please see: https://www.tomreich.com/homepage/projects/simplejournal/
If you are not interested in building the project yourself, you can download a pre-compiled stable version here: https://www.tomreich.com/homepage/projects/simplejournal/simplejournal.zip
Additionally, Simple Journal is available in the Microsoft Store. Search "Simple Journal" in the Windows Store on Windows 10/11.