fasm

Flat Assembler, maintained by the open-source project fasm, is a lightweight x86 assembler whose entire toolchain fits in a single 100 kB executable. Written in assembly itself, it compiles DOS, Windows, and Linux programs from source files that mix Intel-syntax mnemonics with powerful macro directives, enabling everything from tiny boot sectors to 64-bit Windows drivers. Because it requires no installation or dependencies, it is frequently chosen for teaching protected-mode programming, building custom operating systems, and patching existing binaries where every byte counts. Hobbyists embed it in makefiles to generate BIOS extensions, demosceners use its built-in linker to produce 256-byte intros, and security researchers appreciate its ability to assemble position-independent shellcode straight into hex dumps. The package ships with extensive headers that define Windows PE, ELF, and Mach-O formats, so the same source can be cross-assembled for multiple targets without switching toolchains. Users can build bootable ISO images, create flat binaries for embedded boards, or link against C libraries through standard COFF import tables. Flat Assembler is offered for free on get.nero.com, where downloads are delivered through trusted Windows package sources such as winget, always providing the latest build and allowing several development tools to be installed in one batch operation.