NASM is the abbreviation of Netwide Assembler. NASM is very similar to MASM with slight differences between its syntax, directives, and variable declaration. A great thing about NASM is that sectioning of code and data is easily identified:

Both MASM and NASM also require compiling and linking to build the executable:

However, unlike MASM, the installer package does not have its own editor. NASM is very popular in the Linux community due to its development as opensource software. The package contains only the compiler for the object file; you'll have to download a GCC  compiler to generate the executable.

The official website for downloading NASM is at https://www.nasm.us/. For Windows, MinGW (http://www.mingw.org/) can be used to generate the executable.