It's a new version of XashXT, an extended front-end for Xash3D engine. It's includes some new features & bug fixes (read the updated documentation inside for details). Click "READ MORE +" to see some important notes about installation of XashXT (you should install XashXT as MOD for Xash3D Engine, it's not a stand-alone game and also will require some Half-Life resources to work properly)!
XashXT (aka Xash Mod) it's a MOD and developers' toolkit for Xash3D Engine with a set of new dlls, demo maps, other resources, additional tools and documentation, and it should be installed as mod in addition to fully working installation of Xash3D Engine + Half-Life game. It can't work properly without Xash3D Engine files or without some resources from Half-Life. So at first make sure you have DONE THIS before you try to install XashXT. Then extract all XashXT files from XashXT_062.7z into your Xash3D game directory.
P. S. If you need "portable" version of PhysX libraries for realtime physics simulation in XashXT (if you stlii don't have NVidia PhysX driver installed on your PC), it's here. Just extract those files in the main Xash3D game folder or in Xash3D\xash\cl_dlls folder.