One of the more interesting facts (at least to me) about Nitemare 3D is that it was developed by UK indie David P. Gray.
David became somewhat famous from releasing the “Hugo” series of adventure games in the early 90s. His first game, Hugo’s Horrific Adventure (also known as Hugo’s House of Horrors) was put on a lot of shareware disks and ended up on quite a lot of people’s PCs (including mine). I never got very far, but I enjoyed playing the first few bits over and over for some reason.
He later released 2 sequels in the Hugo adventure series before moving on to the 3D action game that Nitemare 3D is.
I found an article about David here: http://www.choicestgames.com/2014/11/where-are-they-now-david-p-gray.html
In this article, he says that developing Nitemare 3D took him 18 months, which was much longer than the 3 months it took to make a Hugo game, which was somewhat disappointing to him. He later moved on to more simple games, such as jigsaw puzzles, perhaps because making a 3D first person shooter on your own proved to be quite a big task.
I found another interview with David here: https://thiscageisworms.com/2013/05/27/david-p-gray-interviewed-by-classicgames/
David maintains a page on his website about these old games, where you can find more info and even buy them 😀
Hugo: http://www.dgray.com/hwpage.htm
Nitemare 3D: http://www.dgray.com/n3dpage.htm