NetWide Assembler (NASM) is an open-source assembler for x86 and x86-64 architectures. It is used to write assembly language code, allowing for the development of low-level programs with total control over hardware. NASM is known for its flexibility, compatibility with various operating systems, and clear syntax. It is a popular tool among systems programmers, embedded software developers, and low-level computing enthusiasts. Its open-source nature has allowed it to evolve over time, remaining relevant in systems programming.