Cube
I had heard about Cube here and there in the past (before hearing about it a ton in the leadup to Splice) and that led me to watch Cube 2 a couple years ago because it was free on demand. That is probably not ideal because in many ways that film is exactly the same as this one (without any acknowledgment). There is one major difference between the two but at the end of the day it isn't a major one.
What is major is the difference between whatever person they got to make a sequel and Vincenzo Natali directing here from a concept he helped bring about. It isn't the most complex concept, you've got a bunch of people and they are stuck in cubes that have doors on each wall attached to other cube rooms of the same nature. You've got booby traps that kill people. The group wants to find their way out and thus need to figure out how to avoid the traps and get an idea of where they are in the broader array. There is just something naturally tense about this set-up.
You've got some good use of mathematical concepts. Of course you've also got fairly marginal acting and a pretty terrible script that is pretty heavy handed with exposition laying out the social and psychological implications. But what made the sequel barely tolerable also makes this one passable (and better for Natali's better ability to visually draw out the tension). Whatever, not a bad time.