Google is capable of just about anything.
.inibin - Leaguecraft textures (at least from what I gathered).
.sco - The SCO file type is primarily associated with 'cSound' by Csounders. cSound is open source sound software.
.skl - Three-dimensional skeleton file used by Maya, a 3D modeling and animation program; defines the basic structure and movements of a 3D character created with Maya.
.skn - The SKN file type is primarily associated with 'eRocket eBook Skin'.
.wgt - Widget that serves as a small Web application for the Opera Web browser; saved as a compressed archive containing a widget configuration file, index document, images, JavaScript files, and style sheets; may be installed by direct download or using the "Add Widget" option in the Opera Widget menu.
.dds - The DirectDraw Surface graphics file format was established by Microsoft for use with the DirectX SDK. The format is specifically designed for use in real-time rendering applications, such as 3D games. It can be used to store textures, cubemaps, mipmap levels, and allows for compression.