The O.G. NESasm assembler for NES 6502 assembly, version 3.1 (Latest as of March 2016). Includes Makefile for OS X / Linux / other Unix-like OSes.
cd source && make && sudo make installThen run the assembler with nesasm.
See usage.txt for more details.
Original source, by bunnyboy, is available here.
The only modification I made is inclusion of the Makefile, which was adapted from the one included with MagicKit, and the text files,
which were found in various places in the aforementioned sites and by lots of research/searching on my part.
