I’m building a journaling app primarily for myself but with a view that others might want to use it to. I’ve built it in rails and deployed it. The experience has been great and it’s the first “app” I’ve deployed outside of work. But I haven’t shared it with anyone because I don’t want to be responsible for hosting their data considering the intention of this app. The only “business model” (method of covering costs) I’m interested in is pay to use. I don’t want to do ads or tracking. I think saas is the wrong fit for it. So I’m just this week thinking about making it a macOS / iOS app instead and work out how to do syncing without involving a server.

"Without using a server" is possible, but hard.

An alternative is "using a server that the user has", e.g. saving to their iCloud/Dropbox/Google Drive/GitHub/etc.

(There used to be old notes applications which would save your notes in an IMAP folder on your email server; almost every user of your app will have email.)