FastMM4 is a production-grade drop-in replacement memory manager for Delphi and C++Builder on Windows. It replaces the default RTL allocator with a multi-threaded, low-fragmentation design organized into three tiers: small blocks (binned by size class), medium blocks (linked-list pools with bitmap-based binning), and large blocks (VirtualAlloc). The core logic lives in FastMM4.pas, a single monolithic unit, with FastMM4Options.inc providing extensive compile-time feature toggles (FullDebugMode, leak reporting, alignment, memory sharing, etc.). This is library code — there is no UI, no data pipeline, and no business logic; the only executables are demo applications (e.g., a Usage Tracker VCL form) and the BorlndMM.dll replacement for C++Builder.