LÖVE

Seems cross-plataform Lua engines are popping out. Don't remember see this one mentioned here.

http://pipmak.sourceforge.net/

EDITED: This isn't real 3D as mentioned in Topic. All are mapped 2D pictures with room changes accomplished by Hotspot Nodes. However interesting Lua project.

• An open-source cross-platform game engine and authoring environment, the Pipmak Game Engine enables you to create point-and-click adventure games in the style of the Myst series, including panoramic ones like Myst III: Exile.
  
  Players of a game made with Pipmak can experience:
  
  Static “slide show” images or full panoramic views (cubic)
  Parts of a view modified by image patches in response to player actions, game state, or dynamically
  Transition effects such as dissolve, rotate, wipe
  Overlays to create head-up displays, inventories, or the like
  Directional sound effects and background sounds or music
  Runs on Mac OS X, Windows, Linux, and possibly other platforms (both authoring and deployment)
  To game developers, Pipmak offers:
  
  Scripting of arbitrary game logic in Lua, an easy to learn, simple, and powerful scripting language
  Freely redistributable and modifiable under the GPL licence, also for commercial projects
  Available documentation: reference manual, demo project that shows all features in action
  Friendly community support on the mailing lists/newsgroups
  Pipmak is still a work in progress. Some of the biggest currently missing features that are planned for the future:
  
  Video – you are currently limited to doing animation by flipping through a series of images or by moving sprites around
  Graphical editing: hotspot painting, project map to draw links between nodes, interactive patch placement
  Compilation of the product into a single file – distribution as a monolithic application bundle is possible on Mac OS X, but on Windows and Linux a distribution-ready game still consists of multiple files
  Making a game using Pipmak is mostly a matter of creating the game’s graphics using a 3D rendering program or other graphics software and then describing to Pipmak how these should be presented and how they should behave in specially formatted text files. Direct graphical editing within Pipmak is planned for the future, but only fragments of it are present at the current state of development. You can, however, edit a project while it is running in Pipmak and immediately see your changes.
  
  As an open-source project, Pipmak welcomes contributions. Bug reports, examples, documentation, community help, code – anything you have to help make Pipmak better is appreciated.

An engine with a very specific but awesome purpose! I will have to remember this.