64tass is cross assembler targeting the 65xx series of micro processors.

Features:
- Open source portable C with minimal dependencies
- Familiar syntax to Omicron TASS and TASM
- Supports 6502, 65C02, R65C02, W65C02, 65CE02, 65816, DTV, 65EL02, 4510
- Arbitrary-precision integers and bit strings, double precision floating point
  numbers
- Character and byte strings, array arithmetic
- Handles UTF-8, UTF-16 and 8 bit RAW encoded source files, Unicode character
  strings
- Supports Unicode identifiers with compatibility normalization and optional
  case insensitivity
- Built-in "linker" with section support
- Various memory models, binary targets and text output formats (also
  Hex/S-record)
- Assembly and label listings available for debugging or exporting
- Conditional compilation, macros, structures, unions, scopes