ASM6 is a command line assembler targeting 6502 processors. It was written for NES development, but is not geared to any system in particular and should be compatible with anything that uses a 6502. The assembler has a flexible syntax, supports local and nameless labels, and has a number of directives to make your code cleaner and easier to read. See the readme for a full list of features. The source code is included in the archive.