Microchip has USB software to support USB on 8-bit, 16-bit and 32-bit MCUs. This software is royalty free source code and also includes example projects.

The 8-bit PIC18 family supports USB device mode. The 16-bit PIC24F and 32-bit PIC32 products with USB support device mode, as well as embedded host and On-The-Go. All product families support up to (FS-USB) full-speed operation (12 Mbps).

USB Stack for 8-bit, 16-bit and 32-bit PIC Microcontrollers is part of the
Microchip Applications Library

The USB Framework is a distribution package containing a variety of USB related PIC18, PIC24F, PIC32 firmware projects, along with other USB related drivers and resources intended for use on the PC. All release notes are included in the .zip file bundle.

Demos include Device CDC demo, Printer demo, bar code scanner demo, CDC serial emulator, device composite HID and mass storage, generic driver demo, HID mouse demo, HID keyboard demo, SD card reader, SD data logger, thumb drive data logger (host) and much more.