Assembler

An assembler takes machine readable assembly instructions such as beq (example - means branch if equal) in its common 3 letter abbreviated instruction and produces the binary code (32 bit instructions usually). Unless someone can read binary this is the lowest level programming language that exists. It is rarely practiced today, unless you are a system programmer. Application programmers use higher level languages these days.

GAS (GNU Assembler) is a common assembler found on most accessable UNIX like system.