Hi,
some times ago I already thought about Machines Mod for any existing game.
The problem is, I know only two games, which have gameplay close to Machines:
- Battlezone II
- LEGO Rock Raiders
- Battlezone II is well modable and has still a small modding community, there are some good modding tools.
The Problem is, In BZII you can go outside the vehicle and act like human, what does not fit Machines idea.
- LEGO Rock Raiders is complety NOT moddable in any way

Since, I have some modding experience with few Q3-based games, I was thinking about this.
The problem is, Q3-Engine is developed especially for First Person Shooter games.
It is possible to create strategy game on quake engine, but than we still need any experienced coder, who can make needed changes.
The best example is "UFO:Alien Invasion" a remake of old DOS game "UFO Enemy unknown" based on Quake2 engine.
http://ufoai.sourceforge.net/?page=HomeSo only one idea, I think is realistic at the moment is "Jedi-Knight Jedi Academy"-Engine.
Why ?
Benefits:
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1. Based on Q3 engine, so we can use all of the tons modding tools av.
2. This engine supports vehicles(ATST etc.) and NPCs, which can act without "pilots"
3. we can build relative big maps with one of the best world editors av., the GTK Radiant.
4. This engine supports scripting.
5. The menu and UI are well moddable
6. we can build completly independent Single-player campaign.
7. There is one of the best multiplayer-code av.
8. Q3 engine is Open Source now.
Drawbacks:
=========
1. Everyone, who would like to play this mod, has to have a copy of JKJA (until we can code our own version based on Open-Source Q3-Engine).
2. Making of JKJA models is not easy, you have to be at least advanced modeller.
3. Only First-Person strategy is possible without codding.
What do you think ?
If you do not like this idea, I have one more, it is Warzone 2100 engine(RTS), it is open-source now.
It is well moddable, but First-Person mode is no possible and the map.editor is horrible.
http://forums.wz2100.net/ (site down at the moment)
Cu, MB