Vanilla Doom has a mysterious command line parameter named "-statcopy". The statcopy parameter allows an external statistics program to capture the intermission screen statistics. However, as far as I know, no such program was ever written. This is, to my knowledge, the first external statistics program ever made for Doom!
On exit, the program displays the captured statistics to the screen, or alternatively saves the data to a file. There is one caveat in that for statistics capture to work, you must have the mouse enabled in Doom (set use_mouse to 1 in default.cfg, or use setup.exe).
Full source code (requires Borland Turbo C) is included.