macOS does have an autohinter, but it only makes very slight changes. More important is the stem darkening (which Apple calls font dilation), which distorts out

macOS does have an autohinter, but it only makes very slight changes. More important is the stem darkening (which Apple calls font dilation), which distorts outlines to make fonts bolder at small sizes. Windows actually has two font rasterizers: GDI, which lived in the kernel prior to Windows 10, and DirectWrite. GDI does no vertical antialiasing, but DirectWrite does. Both do vertical hinting, but only GDI does horizontal hinting. (With ClearType on, GDI applies a hacky subset of horizontal hints--Beat Stamm has documentation on it on his Web site.) FreeType, naturally, can do all of the above (except the GDI hacks), depending on how you configure it.