xPack allows you to create 'Packed Textures' with a clear and efficient user interface to build your Packed Textures, supporting RGBA PNG files and DDS files.
Packed Textures are used in many Game engines, GameGuruMAX, Unity and Unreal, textures need to be at the power of 2 i.e 512x512, 1024x1024 etc.
Each ARGB channel can have different images to create a single 'Packed' Image for example Unity uses a Metallic-Smoothness Map:

RED Channel = Metallic
GREEN Channel = NOT USED
BLUE Channel = NOT USED
ALPHA Channel = Smoothness