In order to be able to make standard USB HID devices (like game controllers, keypads, mice, digitizers) that can talk directly to the operating system, you need to be able to pack odd sized pieces of data together in the way that the PC expects them, like the illustration below: an example that comes directly from the HID Usage Table Specification.

Devices that can pack and unpack like that can talk directly to any operating system: not just Windows, but Apple and Linux, too!

(It's true that HIDmaker FS makes user mode programs "only" for Windows right now, but for devices that talk directly to the operating system anyway, that's not a problem: you can develop your device in a Windows environment, and use your device with Linux or Mac O/S or any other operating system that can talk directly to a HID device.)