This is clownassembler, an assembler for Motorola 68000 assembly language. It mimics the behaviour of SN 68k (also known as 'asm68k').
Being a reimplementation of SN 68k, documentation for that assembler applies to this assembler as well:
http://antime.kapsi.fi/sega/files/SATMAN.pdf
This assembler is written in portable ANSI C (a.k.a. C89), and so should be able to be built with virtually any C compiler.
Before the assembler can be compiled, the lexer and parser must be generated.
Install Flex, Bison, and Make, and then run make in this directory to
generate them.
Once that is done, the assembler can be built with make assemblers.
Alternatively, the assembler can be built using CMake.
Two copies of the assembler will be produced: clownassembler and
clownassembler_asm68k. The latter provides the same command line interface as
SN 68k, while the former provides a custom, simpler, interface.
This is Free Software, made available under the terms of the AGPLv3+. See the 'LICENCE.txt' file for more information.