Metasm is a cross-architecture assembler, disassembler, compiler, linker and debugger.

It has some advanced features such as remote process manipulation, GCC-compatible preprocessor, automatic backtracking in the disassembler ("slicing"), C headers shrinking, linux/windows debugging API interface, a C compiler, a gdb-server compatible debugger, and various advanced features. It is written in pure Ruby.

More information can be found on the Metasm web site