A tutorial on cross compiling for the 6502 CPU
An assembler for the legendary 6502 processor and it's derivatives
multi-platform cross assembler for 6502/6510/65816 cpu
The Small Device C Compiler (SDCC), targeting 8-bit architectures
ATasm is a 6502 command-line cross-assembler.
Cross-platform 6502 assembler
A "Just Enough Language" compiler targeting the 6502/Z80/6809