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/136751/shellsploit-framework-0.2.tar.gz
Source: https://packetstormsecurity.com/files/136751/Shellsploit-Framework-Beta-0.2.html