xa is a high-speed, two-pass portable cross-assembler for the 6502 CPU
with a C-like preprocessor. One of several popular 65xx assemblers, xa
is written in C and released under the GPL-2. It has been in continuous
development since 1989.

Other tools in the xa package are:
* file65 - a tool for printing information about o65 object files.
* ldo65 - a linker for o65 object files.
* printcbm - a simple CBM BASIC detokenizer similar to the far more
powerful petcat proviced by VICE.
* reloc65 - a relocator for o65 object files.
* uncpk - a c64 cpk archive manager.