TiddlyWiki kind of does this. It can store binary data, but it is literally a single HTML file (or at least can be easily saved as such). I think you could just

TiddlyWiki kind of does this. It can store binary data, but it is literally a single HTML file (or at least can be easily saved as such). I think you could just export to a single file tiddler and email that to yourself as a chron job. For sync, I personally just use OneDrive though any other file sync service would work just as well. I use TiddlyDesktop actually and save everything as a single HTML file. TiddlyDesktop has its own backup system separate from OneDrive since it always puts the previous version into a folder before saving over it (this does need cleaning out periodically). The backup feature is actually great for resolving conflicts since the backups have unique names. TiddlyWiki even has encryption, though I've never done it. There is a plug-in for encrypting individual tiddlers as well.