asx is a UNIX-style x86 (IA-32) assembler capable of handling both 16-bit and 32-bit mode instructions. It performs span-dependent instruction optimisation even in the presence of align statements, and features fairly full support for x86 general purpose and floating-point instructions; however, multimedia (MMX, SSE, SSE2) instructions are not currently supported.
Input syntax is mostly compatible with existing x86 "AT&T syntax" assemblers. Output format is 4.4BSD-compatible a.out, as accepted by bsdtools.
Download the distribution file.