libetc2 decodes ETC2_RGB and ETC1_RGB texture formats into raw rgb24 data. It is based off of the Khronos data specification.

UnityPack and pillow did not appear to support ETC texture unpacking.

I was only interested in decoding, and ETCPACK is designed to be built on the Visual Studio platform. This is a decode-only reimplementation for POSIX/GNU99.

You can use it as such:

./etc2tool input.bin output.rgb

And it outputs raw rgb24 data to output.rgb, which can be converted into an appropriate image format using various utilities such as pillow.