It's bizarre that neither the README nor the associated minimal site explains what it does in detail, with screenshots or anything. I'm assuming this is a modern version of GDI++, which a decade ago brought Mac-style font rendering to Windows, but stopped being maintained a while ago. For people who aren't aware of the difference, it's essentially that Windows uses heavy font hinting to try to align character strokes…
This was ten years ago, so dunno if anything has changed.