Shellsploit lets you generate customized shellcodes, backdoors, and injectors for various operating systems. It also has obfuscation abilities.
You can download it from the following link: https://packetstormsecurity.com/files/download/137171/shellsploit-framework-0.3.tar.gz
Source: https://packetstormsecurity.com/files/137171/Shellsploit-Framework-Beta-0.3.html