I just use an editor and a local git repo. Write everything in Markdown. Current editor of choice is Pulsar but use what you like. Self hosted repo lets me access the notes from any device as well as keep a history of what I've changed.

I'm a big fan of Obsidian. It's not open source, but it's free forever and has a rich theming and plugin ecosystem, and it works on just regular markdown files in folders so you're not locked in by proprietary file formats or anything, you can switch to basically anything that edits text and lose nothing. There's paid sync and publish features, but because it's just ordinary text files, you can replicate those for free with OneDrive and Jekyll, or your favourite tools of similar function.

Maybe Joplin?