GemRB is described as '(Game Engine Made with preRendered Background) is a portable open-source reimplementation of the Infinity Engine that underpinned Baldur's Gate, Icewind Dale and Planescape: Torment. It sports a cleaner design, greater extensibility and several innovations' and is an app. There are more than 50 alternatives to GemRB for a variety of platforms, including Windows, Linux, Mac, Web-based and Android apps. The best GemRB alternative is Godot Engine, which is both free and Open Source. Other great apps like GemRB are Unity, Unreal Engine, GDevelop and Wick Editor.