Here you will find some useful links and tutorials on how to work with the HPL1 engine in terms of modeling, audio editing and even animation.

All 3D modeling packages require the option to export in the Collada format, regardless what program is used.

1. Alias Maya - The world's most powerful integrated 3D modeling, animation & rendering solution.
2. Autodesk 3D Studio Max - A professional 3D computer graphics program for making 3D animations, models, games and images.
3. Blender - Open-source 3D modeling program that comes with built-in support for Collada

1. Adobe Photoshop - Professional image editing software.
2. GIMP - Open-source 2D GNU Image Manipulation Program.

1. Audacity