Shellter is a closed-source project, but if you really like it and you want to have a look at its internals then you can buy the source code. You can choose between community and Pro builds source code.
However, it is recommended to get the source of the Pro build as that is the one actively maintained with feature additions, and code clean-ups.
Why should you pay for it?
Shellter is the most advanced PE infector/Shellcode Injector ever created. Buying the source code gives you access to the spirit and soul of this project. You can then use the whole or part of the source code to create your own private PE infector on steroids to use in your InfoSec adventures.
This is the real deal!
Terms and Conditions apply.
You may contact me for any questions that you might have, but I will only reply to emails sent by legitimate companies and/or organizations.