SLCacheViewer is a Windows application that allows you to browse and export textures stored on your hard drive by your Second Life viewer. All of the major viewers store their texture cache in the same format, and this tool is designed to read that format.
I have received a huge number of emails recently about the program not working with the latest viewers. I cannot possibly hope to respond to everyone individually. I will look and see what has changed as soon as I have some free time and see if it is possible to update the program.
In the main view, you can see all of the textures your viewer has cached.
In the image dialog, you can inspect a texture more closely.
In the sculpt dialog, you can see how a sculpt texture might look in 3D.