FW: Machine Code

Is it possible to write machine code instruction directly to the
computers memory without using an assembler? Is there an open source
"binary file" editor that someone can recommend that will allow me to do
this?

Do chip manafacturers typically provide an assembler that compiles
assembly language instructions into the machine code for there
processor, or does a programmer have to rely on third parties for the
assemblers?

I'm just wondering if it is possible to write a machine code file
directly without the need for an assembler.

Landon