The Open Source solution which serves me well for years has been TiddyWiki (1). Supports Tags and various modes of output. Each page one file or all in one, very open so recursive changes can be applied on the shell in plain files.
I was a big user of TiddlyWiki but Obsidian has so many UI quality of life improvements, and the plugin ecosystem is evolving at such a rapid pace that I decided to jump ship.
I wrote a guide on my migration process: https://forum.obsidian.md/t/import-from-tiddlywiki-5-to-obsi...
That's an interesting name for an open source project. :P