I recently started working on an oldschool 3D game project based on Wolfenstein 3D. The first idea was to recreate old good game engine from Wolfenstein (and in later time also from Doom and maybe Quake) in Unity 3D. Then it cames idea of creating full game because making any engine You need some gameplay to test it. So I'm creating Wolfenstein 3D's clone (I'm not going to make it the same as the original) concentrating mainly on the engine/editor part of it.
Currently I'm working on level/map editor and actors (sprites, AI).