free assembly compilers
NASM is the Netwide Assembler, a free portable assembler for the Intel 80x86 microprocessor series, which uses the traditional Intel instruction mnemonics and syntax.
The NewBasic Assembler, NBASM, is an x86 assembler and is near MASM 5.1x compatible. NBASM is intended for use by beginners starting to learn assembly. NBASM is easy to use and is a great start for learning assembly. Once you have exceeded NBASM's capability, with NBASM's syntax, it is very easy to move on to another assembler.
A masm32 IDE by Justin Decker and Clive Crous