A USB stack for a HID class device on a PIC18 (PIC18F2550) microcontroller.
I started working on this because the USB was interesting and all the devices using a serial-to-USB instead of a proper interface always seemed too hacky. The default Microchip USB stack, now a part of Microchip Libraries for Applications, suffers from bloat of supporting too many different devices and modes of operation (USB OTG in a 8-bit MCU?) even if the code was nice and readable.
Anyway, it has been a nice educational experience. This code enumerates correctly and the most recent effort was on getting the HID class reports working. Unfortunately, Raspberry Pis and Arduinos made making small, connected peripherals much easier, and it's hard to justify putting more effort into bringing this project to completion at this point. If you want, fork it and use whatever's already there - USB descriptor management, control endpoint and enumeration processing, and beginnings of HID support.