JWasm!

The Netwide Assembler, NASM, is an 80x86 and x86-64 assembler designed for portability and modularity. It supports a range of object file formats, including Linux and *BSD a.out, ELF, COFF, Mach-O, Microsoft 16-bit OBJ, Win32 and Win64. It will also output plain binary files. Its syntax is designed to be simple and easy to understand, similar to Intel's but less complex. It supports all currently known x86 architectural extensions, and has strong support for macros.

Pelles C is a comprehensive development suite that can help you create apps compatible with Windows and ARM platforms.

Easy Code is the visual assembly programming environment made to build 32-bit Windows applications. The Easy Code interface, looking like Visual Basic, allows you to program Windows assembler applications (executable files, dynamic and static libreries, COFF object files, console applications and drivers) done in an easy way as was never possible before. Download and test this application including the source code of a nice CD player, a complete and fast text editor in a dll file (to be able to program your own editor), a complete and excellent text editor ready to use, a file shredder, a MIDI player and many other applications. There are two available versions of Easy Code: »

MASM Builder is a free Integrated Development Environment IDE for developing 32-bit Windows programs using the Assembler. MASM Builder contains many useful features which will assist you in creating Windows API based programs.