LZASM

Lazy Assembler (LZASM) is a freeware, TASM IDEAL mode compatible assembler with 32-bit binaries for DOS and Windows. Its output format is OMF and supports MMX, SSE, SSE2, SSE3 (PNI), SSE4 (MNI), and 3DNow!Pro instructions.

The current version is 0.56 (as of 6 Aug 2007).