Files with the extension .VMF are 'Valve' map files created within the 'Valve Hammer Editor'.

The .VMF format is a proprietry format used to store raw map data, and contains details of map brushes, game entities, etc. in a script format.

.VMF files are commonly related to games used by 'Steam' such as 'Counter-strike' and 'Half-life'.

Steam is a digital distribution system and multiplayer gaming and communications platform.