Originally, NASM started out as a copyrighted program similar to FASM. Recently, however, NASM's original authors released NASM to the open software community under the LGPL license. Hopefully, this will encourage future development of NASM as development of the product has seemed to stall for the past couple of years (with lots of NASM users defecting over to FASM).

Though NASM is a bit slower than many other assemblers, it does have a couple of postive features: first, it has been around long enough to have been shaken down and for this type of product, is relatively robust. Second, there are several books and tutorials (including a book by Dr. Paul Carter, available here on Webster) that use the NASM syntax (for Windows, DOS, and Linux). Another big advantage to NASM is that it runs on almost every x86 operating system that has graduated beyond the "toy" level. This includes many OSes for which few other assemblers are available (e.g., QNX and BeOS).

You may download NASM directly from Webster (see the links below). You can also grab NASM off its sourceforge home (see the links below), though the version here on Webster is probably the latest (as NASM doesn't change very often).