It took a while because of some difficult technical challenges, but I've now integrated a physics engine into Outpost. I still need to fix up some weirdness in player movement code that uses it but all the base stuff to make it work is in. Here's an obligatory colliding cubes demo video (not a preview of actual game content, just a test to make sure the physics engine is working properly)
I've also added a floating feature. Press F to start floating. There's a very limited maximum altitude, and you'll burn your thrusters out and fall a bit if you go too high above the ground. The player can extend it later, but for now I need a flying feature so that I can improve movement code a bit, for example so that the player can't walk up steep mountainsides.