Back in the days when Microsoft Game Studios was a real and active presence that gave us games like this, Mechwarrior 3, Outwars, and Crimson Skies, Allegiance was one of the first multiplayer oriented space sims to come out. Designed to work with the now defunct Zone multiplayer service (God, I'm old. Hey, remember MPlayer? or Kali? Or Gamespy?), this game offers an RTS/FPS mixup like no other. Think less Natural Selection and more like X-wing versus Tie Fighter, but each side has evolving tech trees. Strongly recommended!
The two main methods of play are as a combat pilot, or as the commander of the team.
AS A PILOT:
Your job is to be one of the grunts you order around with Right Click in an RTS. The commander is supposedly in charge, but, uh... if you've been on the internet for any amount of time you know how the general public reacts to any kind of authority giving orders. The team's success now rests in your sweaty, possibly anti-social hands. God help us all.
This is a space combat game, taking place on a large map with several smaller zones connected by gates. There are semi-newtonian physics involved during normal flight. There are max speeds, but WASD lets you use lateral thrust, and afterburner slides are a recommended tactic.
Your piloting goals are to kill enemies (or just force them to eject, which is really inconvenient) and keep the team's economy going long enough to get stuff to kill bases with. To win, destroy all the enemy bases. Harder than it sounds. You can fly defense as an interceptor, or deploy proximity mines to ward off assaults, but winning requires that you take the offensive in bombers or escorting capships.
Similar to C&C Renegade, another FPS/RTS, there are AI miners who try and mine resources for money. If you manage to keep them from being annihilated, they eventually return home and give everyone a cash payday. If they take too much damage, they get cold feet and run for home with empty cargo bays, so keep a close watch!
In true classic RTS form, there are powerups and cash drops, so your awareness and pilot skills do make a difference, even in the economy! Even if you think you suck, you can still contribute just by spotting enemies and harassing miners.
AS A COMMANDER:
Congratulations! As the only person with some semblance of authority, you are now the first person to be blamed for everything.
Assuming you haven't been scared off, being a commander is not really so difficult. Your job is to be the omnipotent RTS commander, with the caveat that you can only order Miners, Constructors, and automated non-player objects. You may not be able to control a player directly, but you can give them orders, make suggestions, call out sectors, and are directly commanding how the game goes for your team. You tell the miners where to go to mine Helium 3 (Money) and other special resources to build new bases. You also control what to build, where and when.
To win, you need to expand into other sectors and get down your tech tree as fast as possible in order to take down enemy bases. You can build several different types of bases, which sometimes requires special asteroids. This means that you are always feeling some kind of pressure to expand and attack certain sectors - money alone won't win it for you!
You automatically get money when the miners return home from harvesting. The tech tree is quite involved and actually varies depending on the faction you're in. Iron Coalition has better fighters, BIOS have faster scouts and stealth, just to give a couple examples.
You're not chained to the command console, and can always go and lead the charge. You can access the command console mid-flight, but be warned you will make a highly tempting target for any combat pilots.
A fine space action game desperately in need of an official sequel, featuring involved RTS mechanics, great skill-based combat, and a varied game experience with different factions and maps. Strongly recommended. Especially if you still have your Microsoft Force Feedback 2 joystick.