Cell2D is a free, open-source Java library for making 2D games, designed to simplify and speed up development by handling common organizational tasks. It is based on and incorporates Slick2D.
I was motivated to create Cell2D after I and many other students in my high school AP Computer Science class chose to create video games for our final projects, but not one of our groups completed its respective game by the deadline despite the simplicity of the games' concepts. My group spent a lot of time programming basic event-scheduling and input-processing systems that are common to a lot of games when we could have been working on actual game mechanics, and we still got farther than anyone else, so the other groups likely had the same problem.
I created Cell2D in part to help people like those students, who have some programming experience but are newcomers to game development, to get started quickly without reinventing any major wheels first. I also want to make Cell2D well-documented enough to prevent its users from struggling too much with unexpected quirks, as well as provide enough optional low-level control to allow pros to optimize the environment for their specific game.