tavrasm is an assembler for the Atmel AVR family of micro-controllers. 
It uses a syntax similar to the one found in the Atmel AVR DOS assembler.
Some of the features includes:

    - Super-set of Atmel AVR assembler. 
    - Macros in macros. 
    - Save Intel HEX, Motorola S-record, Generic and binary output. 
    - More than 100 warning/error messages. 
    - Atmel object files compatible with Atmel's AVR Studio. 
    - C escape characters in char/string literals. 
    - Runs on (win)DOS, Linux, OS/2, Solaris, ...
    - Free software released under GPL.