RosAsm is a 32-bit Win32 x86 assembler developed by an independent group of programmers and contributors. It is the continuation of an assembler called SpAsm, always under the direction of its original author René Tournois.

The name stands for ReactOS Assembler, meaning that it was designed to run on that platform as a primary operating system, although both projects are developed by an independent group of developers, not related to each other. ReactOS package does not include RosAsm assembler, and uses itself to assemble part of their sources.

RosAsm is an assembler with full integration of an IDE, resource editor, debugger and disassembler. The syntax is inspired by NASM's.

Site: http://rosasm.freeforums.org