btop++ is a cross-platform system resource monitor implemented in modern C++ (C++20/23). It provides a real-time terminal user interface displaying CPU, memory, disk, network, process, and GPU utilization. The architecture is modular: a main thread handles input and rendering while a runner thread periodically collects system metrics via platform-specific collectors (Linux: /proc, /sys, perf_event_open; macOS: sysctl, SMC, IOReport; BSD: kvm, sysctl). The codebase features a theming engine with gradient support, a config system with TOML-based persistence, and bundled fmt library for type-safe formatting. While the project demonstrates solid engineering with RAII patterns, atomic locks, and terminal escape code abstractions, it relies heavily on global state and platform-specific ifdefs, which limits testability and portability. GPU monitoring supports NVIDIA, AMD, and Intel integrated GPUs through dynamic library loading and kernel interfaces.