The source for the engines of the first three quake and doom games were open sourced. I purchased those games after that happened. Worth mentioning that the

The source for the engines of the first three quake and doom games were open sourced. I purchased those games after that happened. Worth mentioning that the engines were open sourced, not the assets. The assets are obviously a big part of the experience. But if not for the open source versions of their engines (prboom, ioquake3, etc) I'd not be playing these games today.