; NASM Documenation
The NASM documentation is auto-generated on every new release (including release candidates) and accessible either online or in various offline archives. Such archives provide documentation in the following formats: pdf, ps, txt, html, info.
If you are not sure how to unpack these offline archives consider using 7-Zip file archiver. It supports quite a number of formats (including ones provided here). And hey, 7-Zip is open source after all!
; Online Documenation
NASM online documentation is here.