ChatSphere is a feature-rich, cross-platform chat application built in C++, developed by extending a fork of cjchirag7/chatroom-cpp. We transformed the original codebase by fixing Windows compatibility issues and making it work seamlessly on Windows, Linux, and Unix. The project now supports multiple chat rooms, private messaging, and timestamped messages. Users can format messages using bold, italic, and underline, enhancing chat readability. This project showcases strong skills in socket programming, system-level C++, and improving real-world open-source software using both engineering insight and AI assistance.