The .grp (group) file format, used by the game Duke Nukem 3D, is just a collection of a lot of files stored into 1 big one. The Build engine, upon which Duke Nukem 3D was constructed, went on to become one of the most successful engine in terms of number of games released. Other notable games developed using the Build engine include Witchaven, TekWar, Shadow Warrior, Blood, PowerSlave and Redneck Rampage (check for a more complete list and more stuff about the Build engine at http://www.icculus.org/BUILD/). Thus, all of them use the GRP file format
So, here is the plugin I wrote for the Total Commander (TC for short) to access .grp files directly. It is able to list, unpack & pack GRP files (file deletion is unsupported by the format itself...). By the way, this TC plugin is the first one (and probably the only one ever ) to be written in the pure assembler language. I suppose that it's also the smallest TC plugin, with it's 5.5 KB size! And here's a screenshot showing it in action (opening the DUKE3D.GRP).

Installation:

The same as for most TC packer  plugins:

1. Unzip the grp.wcx to the TC directory (usually C:\totalcmd)
2. Choose 'Configuration - Options'
3. Open the 'Packer' page
4. Click 'Configure packer extension DLLs'
5. type grp as the extension
6. Click 'new type', and select the "grp.wcx"
7. Click OK