In no specific order and not a full list, this we have only added to a bit here and there when we have had time.
All 3D models regardless of program used must be able to export to the COLLADA format.
Gimp - Open-source image editing.
Paint.NET - Closed-source free image editor comparable to GIMP but easier, smaller, faster
Audacity - Multi-channel sound editor.
OggDropXPD - Drag'n Drop your audio files to convert them to .ogg.
notepad++ - Advanced text editor, crucial for script writing.