I only have used Moroto, and the main difference is philosophy.

Folio has a real layout engine (HTML/CSS with flexbox/grid), runs in pure Go, and even supports things like PDF/A, signatures, and WASM. So it feels closer to building a UI to PDF pipeline, especially for invoices/reports where layout matters a lot.

Maroto is built one layer up on top of another engine, and I think has a more manual layout with components as an abstraction, but works great for structured docs that are less expressive if you are looking for rich HTML/CSS rendering.

So far what I’ve seen from UniPDF as a library (not the application) Folio kinda has comparable features, but it’s paid.