does anyone know a simple app that allows hyperlinking within notes? I want to create a roam-style knowledge base, but most tools are too heavy for my purposes. I prefer to keep things cross-compatible and future proof with .txt or .rtf, but to my knowledge, neither allow hyperlinking to documents

It supports markdown formatting, does hyperlinks pretty well (even jumping back and forth is quite nice), is as cross-compatible as Vim and stores the notes in future-proof .md files.

I suggest you give it a shot.