If youre not a big fan of storing your notes on a third-party service like Google Keep or Evernote, Paperwork is similar software thats open-source that also allows you to host it yourself.
Paperwork isnt nearly as complex as something like Evernote, but it does have a lot of the more useful features.
you could create various notebooks to store you notes in, build a tagging system, support multi-media uploading, and use WYSIWYG editing.
There arent any mobile apps or anything, but if youd prefer to keep your notes in your own hands, its a pretty solid alternative.
Paperwork| GitHub