Wikipedia
Yasm
In computing, Yasm is an assembler and disassembler for the Intel x86 architecture. It can be used to write 16-bit, 32-bit ( IA-32) and 64-bit ( x86-64) programs. Yasm is a full rewrite of Netwide Assembler (NASM). Yasm can generally be used interchangeably with NASM and supports the x86 and x86-64 architectures. It is licensed under a revision of the BSD licenses. it was developed by Peter Johnson and Michael Urman.