Splines, in mathematics and code, is ' a numeric function that is piecewise -defined by polynomial functions, and which possesses a high degree of smoothness at the places where the polynomial pieces connect (which are known as knots ).' What this does in videogames is make something like a loop de loop run its course automatically irregardless of the speed or momentum you were carrying until you hit the beginning point of the loop de loop. Before modding Sonic Generations was a cool idea, you'd see a whole lot of people port levels over to GDK instead considering that since its inception it could do both 3D and 2D albeit with a bit of scripting via splines. First started by Xaklse, this engine has grown to have many, many contributors building on this engine for the six years and counting since its release. First released on 2010, February 10, the Sonic Games Development Kit has been a collected code source for anyone in the Sonic fanbase at large to develop their own 3D Sonic the Hedgehog fangame. So, Sonic GDK, starting with a bit of history. I've been looking to make sure and apparently no one except a few people are talking about this in a general thread or status update and considering that GDK is fanmade I felt it belonged here.