Associated .GCF software

Windows
GCF file extension
Steam local stored files i.e Half-Life1+2
The Program GCFScape can be used to open these files :
GCFScape is an explorer like utility designed to allow users to browse Half-Life packages and extract their contents. GCFScape supports .bsp, .gcf, .pak, .wad and .xzp packages and runs independently of Steam.