Skyscraper aims to be a fully-featured, modular, 3D realtime building simulator, powered by the Scalable Building Simulator (SBS) engine. The main feature SBS provides is a very robust elevator simulator, but also simulates general building features such as walls, floors, stairs, shaftwork and more. Many more things are planned, including gaming support (single and network multiplayer), and a graphical building designer. Skyscraper is written in C++ and uses the Crystal Space 1.4 graphics engine, the wxWidgets GUI library, and is multiplatform. The current versions aim for a future 2.0 release.
Source: The Game Website.