Asm6502 is an old 6502 assembler written in C. It appears to have been ported to CP/M at one time and it is generic enough to work on anything with a reasonable C compiler. I've compiled it under Unix (gcc) and include here a Macintosh application. PC people, you are on your own, but should have no trouble with it.
I assume this is in the public domain. If you are the author and want to complain let me know.
asm65.tar.gz is a simple 65C02 assembler in Perl. It is primitive but will output code in a format suitable for 'exec'-ing on an Apple II computer. Do with it as you please.