Stratagus

Here are some graphics that someone could try to stick into stratagus(though the non-32*32 terrain tile size would need some accommodation , which is possible as seen in windgus. There are other graphics that could be useful as well. The fire and explosions look interesting) :
http://www.lostgarden.com/files/HardVacuum.zip

The author stated: "Use them, abuse them. If you make anything interesting, let me know. ":
http://www.lostgarden.com/2005/03/game- ... acuum.html

How about, a post apocalyptic survival game? You control one guy and must make it off an abandoned planet (or maybe sent a distress beacon). He can enter buildings and vehicles, taking control of them.

The map can be littered with destroyed buildings, bases and resources. You have decide what you'll focus on gathering and repairing. You can search for information on why a particular building was abandoned/lost to see if its worth repairing, or you can just yolo it and repair everything you find.

Enemies to start with will be nature and wild creatures, although you may accidentally create an enemy faction by activating an insane/enemy robot.

Situation Ideas:

You come across a destroyed military outpost. You repair a number of robots which proceed to repair their base. They mostly ignore you and go off consuming most of the resources in the area, forcing you to move on. Later, you might come across another base and activate it. They start repairing themselves, but then attack the previous base. You can sweep in after the oilshed and scavenge all the left over resources. If you bothered to gather intel, you might have learnt the weak spots of the factions, and exploited them to gather fully functional equipment (say, you destroy the hivemind when it is distracted, allowing you to steal a tank).

You come across a massive abandoned mining base. You waste a huge amount of resources repairing it. Once repaired, you discover that it was abandoned because it had run out of ore. Intel gathering might have allowed you to avoid this situation, and might even have allowed you to find some ore harvesters you could have setup elsewhere.