I was just reminded that markdown+pandoc is a kickass, open source combo that not everyone might be aware of.
Markdown is a super simple rich text markup language that I use every day for notes, recipes, instant messaging, and longer texts like essays and blog posts. It's even supported on most Mastodon instances.
Pandoc is an "under the hood" tool that allows you to convert any document to pretty much any other format worth using. It supports bibliographies and citations in markdown files.