RuneScape today is unrecognisable from its original implementation back in 2001. It has been through several engine overhauls, and has long since moved away from its 2.5D roots. "RuneScape Classic" is now used to refer to the original version of the engine, before the first major 3D update (originally known as "RuneScape 2").
This project was an attempt to refactor the RuneScape client source code to make it easier to understand and maintain. Now, this repository remains purely as a reference.
Further information can be found here.
A list of useful links can be found here.