The GNU Assembler or GAS, or simply AS, is the most used assembler on *nix (Unix and Linux) platforms. While it is cross-platform (having the right build of GAS, we can compile Assembly code for a wide variety of platforms including Windows), flexible and powerful, it defaults to the AT&T syntax, which is, for those used to Intel syntax, weird, to say the least. GAS is free software released under the terms of GNU General Public License v3.