AMD

AMD is just a GMO with a special header. It can contain model, animation and texture data. Files of this format always have a .amd extension.

Noesis
Noesis is a free tool for viewing and converting between hundreds of model, image, and animation formats. It utilizes a robust plugin system, with support for native extension modules and Python scripts.

Noesis is a helpful tool due to its simple GUI.

Noesis allows you to convert AMD files into many common model formats. It also includes a batch option.

GMO2AMD
GMO2AMD is a Python script that allows to add the special AMD header to the GMO model. It also has a Commandline .exe format if you don't have Python installed. Simply drag and drop the GMO file you want to convert to AMD onto the amd.py or the program's exe to convert it.