C-Dogs SDL is a port of a top-down shooter originally developed for DOS.
Over the years of it's development, Cong Xu has added a number of features and extras on top of the original, and with the "full" release of the port came one of the coolest of all; compatibility with Wolfenstein 3D.
If you own a copy of Wolfenstein 3D or Spear of Destiny on either Steam or GOG, C-Dogs SDL will automatically add the games as full campaigns within it. The campaigns use the datafiles of whichever game you run to generate the content; using special Wolfenstein-themed graphics and characters to recreate the experience.
The shareware version of Wolfenstein 3D will also generate a campaign to play, though it will naturally only span 10 levels instead of the full 60.
It's a fun way to re-experience the games and because of the way it handles files, many mapsets for Wolf3D will actually work with it, providing even more C-Dogs SDL content by default!