metame is a simple metamorphic code engine for arbitrary executables.
From Wikipedia:

Metamorphic code is code that when run outputs a logically equivalent version of its own code under some interpretation. This is used by computer viruses to avoid the pattern recognition of anti-virus software.

metame implementation works this way:

1. Open a given binary and analyze the code
2. Randomly replace instructions with equivalences in logic and size
3. Copy and patch the original binary to generate a mutated variant

It currently supports the following architectures:

• x86 32 bits
• x86 64 bits

Also, it supports a variety of file formats, as radare2 is used for file parsing and code analysis.
Example of code before and after mutation:


Hint: Two instructions have been replaced in this snippet.
Here another example on how it can mutate a NOP sled into equivalent code:


Installation

pip install metame

This should also install the requirements.
You will also need radare2. Refer to the official website for installation instructions.
simplejson is also a "nice to have" for a small performance boost:

pip install simplejson

Usage

metame -i original.exe -o mutation.exe -d

Use metame -h for help.