There are 2 repositories under backdooring topic.
Watermarking Deep Neural Networks (USENIX 2018)
Executables created while writing "Introduction to Manual Backdooring".
Basic tool to automate backdooring PE files
Windows/Linux - ReverseShellBackdoor Framework
Ransomware example on Python, created during containment for educational purposes
This Discord Rat give you the best way to control victims pc on discord.
Simple backdoor using lib python's socket and subprocess for Windows
Backdoor for Windows Mobile Phones
A simple but dangerous backdoor built as a kernel module.