This is a distribution of NASM, the Netwide Assembler. NASM is a
prototype general-purpose x86 assembler. It will currently output
flat-form binary files, a.out, COFF and ELF Unix object files,
Microsoft Win32 and 16-bit DOS object files, OS/2 object files, the
as86 object format, and a home-grown format called RDF.

Also included is NDISASM, a prototype x86 binary-file disassembler
which uses the same instruction table as NASM.    

http://www.cryogen.com/Nasm