Infinity Engine

Baldur's Gate (1998) introduced it: pre-rendered 2D backgrounds in an isometric view, sprites for the characters, and real-time-with-pause combat on top of AD&D rules. Black Isle licensed it for Planescape: Torment (1999) and Icewind Dale (2000).

The engine was data-driven enough that fans built mods with their own tools, and much of the rule logic lived in scripts rather than code. Two afterlives remain: GemRB, an open reimplementation that runs the original game files, and Beamdog's Enhanced Editions from 2012, built on the original source.