Allegiance! Now there's a name I haven't read in a long time. tried to get into that community around the time the first Free Allegiance release happened, but I didn't end up with the right combination of personality and time to get really involved, and even though I think the gameplay might be more my jam today, I think the community has largely dried up, and I don't have nearly the time I used to for gaming. (A few years later, I got DEEP into ArmA and DCS, which led my career into academic research connected to defense training and simulation.)

Incidentally, this is another reason to be excited about the second coming of Microprose -- I'm unclear on the exact relationship, but I believe I read that some of the same leadership responsible for TitanIM is associated with the new Microprose.

TitanIM is a defense simulation engine, using Outerra, which is a world-scale 3d+terrain engine. Tech demos of Outerra are around, and there's at least a few TitanIM videos floating around. I've been out of the sim/training niche for a couple of years, but I believe Titan is still being marketed as a competitor to Virtual Battle Space (VBS) which is the ArmA engine, but expanded and specialized for training, and sold into government with the associated contract support, etc.

I have no idea if this overlap in leadership means Microprose might have access to/be using the same tech stack as Titan for the new Microprose games, but if they are, it could be pretty darn cool.