Other Protocols (Network & Wire Protocols): open-source projects that exist because someone reverse engineered a closed product, sorted by GitHub stars.
Open source Spotify Connect client library in Rust
.NET library interoperating with Valve's Steam network protocol
Tracks Steam client files, protobufs and API changes for research
Reverse-engineered Chrome's private X-Browser-Validation integrity header; generator toolkit
Simple Synology package server reverse engineered from the official package repository protocol
Reverse-engineered news helicopter downlink radio protocol from audio in video
Reverse engineered implementation of the Chirp data-over-audio protocol
Android NFC reader demo for Apple VAS and Google Smart Tap protocols
Ruby library for interacting with an AirVideo server
Reverse engineered lightweight cross-platform FRC Driver Station
Open FSD multiplayer flight simulation network server
Auto generated messages for the World of Warcraft network protocol
Demodulate and dissect RF packets from E-ZPass toll transponders
Reverse engineering and reimplementation of the Windows NT kernel debugger protocol
World of Warcraft Wireshark dissector
Library for World of Warcraft flavor of SRP6 authentication.
Reverse-engineered Streamate webcam protocol; native client
Library for the Microsoft Media Server (MMS) streaming protocol