Here you can find the list of shellcodes developed in this blog, I always suggest to do not download and execute it but to take it as an example/help to write your own shellcode, if you really don’t resist to run this code, do it in a develeopment environment. In any case I’m not responsible for what you do with this shellcodes.
Some codes published here are also on Exploit-DB

Linux

• Linux/x86 - adduser (User) to /etc/passwd Shellcode (74 bytes)
  
• Linux/x86 - execve /bin/sh Shellcode (25 bytes)
  
• Linux/x86 - Reverse Shell NULL free 127.0.0.1:4444 Shellcode (91 bytes)
  
• Linux/x86 - NOT + XOR-N + Random Encoded /bin/sh Shellcode (132 bytes)
• Linux/x86 - execve() - Alphanumeric (66 bytes)

Windows

• Windows x86 - spawn calc.exe Win7/10 (176 bytes)
• Windows x86 - spawn custom MessageBox Win7/10 (223 bytes)
• Windows x86 - spawn reverse shell Win7/10 (387 bytes)
• Windows x86 - hashed reverse shell Win7/10 (222 bytes)