FIFE Engine
For the ones that have never heard about FIFE: this project is an open source engine that aims to be a platform for the creation of 2D RPGs. We do also provide support for the assets of the original Fallout games. So FIFE will be a good choice for the creation of Fallout-like & even non-Fallout-like games under all major platforms (Linux, Windows, Mac) with the emphasis on easy modding.

Link: Aici