I intend for this to be a compilation of all information regarding the campaign multiplayer mode in MGSV, known as Forward Operating Bases or FOBs. FOBs are separate from Metal Gear Online (MGO), and as we know very little about those systems, I'll leave them for another topic.

Feel free to add/correct any information you know about.

General Info:

• FOBs are developed in your single player campaign, using resources that you've gathered and soldiers you've recruited. You can customize the defenses and staff to some degree.
• FOBs generate resources that can be used to develop your Mother Base.
• Your FOBs can be attacked by other players (and in turn you can attack others), but your single player home, Mother Base, can never by invaded by other players.
• The invasions are always 1v1.
• You receive an alert that your FOBs are under attack while you are playing, and can pause the mission you are on to go and defend your base.
• Your FOBs can be attacked while you are offline. Players on your friends list can help defend your base in your stead.
• You can take your FOBs totally offline, rendering them unable to be attacked, but you cannot attack anyone yourself. It is rumored that you will not accrue any resources as well; this mode may be intended to allow you to edit your FOBs layout without the fear of an attack.

Attacker Specific:

• As the Attacker, your goal is to travel from your breach point to the marked Platform Core, stealing resources and kidnapping personnel along the way.
• You have a limited amount of time to do this before the surrounding waters are blockaded and a clean escape becomes impossible.
• You only have one life; getting killed or Fulton'd by the defenders is an instant failure. This may negate any resources gained, or you may keep what you've taken so far; it isn't known yet how that's handled.
• Getting detected by the AI will spot you for the defending player; staying out of sight for a period of time will remove it.
• If you are never detected and make it to the goal, the defender will not learn the location of your FOBs or be able to directly retaliate against you.

Defender Specific:

• You are notified as soon as someone invades your FOBs.
• You may be aware of the general location of the attacker, but will not know the exact position until they are spotted (either by you or your AI defenders).
• Capturing or killing the attacker results in an instant win, getting neutralized yourself will allow you to respawn as a different character. The invasion continues until the timer runs out, the attacker is neutralized, or the attacker reaches the goal.
• As long as the attacker is spotted at some point, you will learn the location of their FOBs, allowing you (and your friends) a chance to retaliate and take back what was stolen, materials and guards included.
• Fultoning wounded guards prevents them from dying.
• Gas mines and CQC (among other things) can render you temporarily unconscious, forcing you to relocate the attacker once you wake up.

Other tips:

• Certain items have specific effects that manifest only during FOB invasions; for instance, the Stealth Camo cannot be used at all, and the Sneaking Suit prevents NVG equipped troops from seeing your heat signature.
• You can assign specific areas of your FOB with guards and traps, or let the game handle the placement.
• You have a limited amount of time to rescue your stolen guards before they are converted to the enemy's service. They are Big Boss too, after all.
• The currency known as MB Coins makes an appearance. It's hard to tell if this is a purely microtransaction based currency or can be earned in game, and what it does to the FOB system in particular (it may prevent you from operating more than one FOB without paying).
• There is a specific Espionage score that goes up when you silently knock out guards and steal resources and goes down when you kill them, have things stolen from you, or are knocked out yourself. This may play into an overall leaderboard or may factor into some kind of post-invasion reward.

That's all I can think of right now. Feel free to point out what I missed or what needs changing and I'll add it to this post.

Here's the video that OP pulls screen from, in case you wanted to see the scenarios in action, thanks for the handy summary!

It all sounds great other than the alerts, I don't want a FOB invasion alert when I'm doing a really important story mission/boss fight.

@flstyle: You can turn off the invasion function whenever you like, so you could always deactivate your FOBs right before tackling a story mission, and turn it back on when you are freeroaming/doing a side op.

@mirado: Thank goodness for that!

Metal Souls.

People are missing the most important reveal from the trailer: there's going to be a weapon named Fist of Jehuty!

Also didn't know that you can be a not-Snake character, but after keeping the Peace Walker base-building mechanic I guess it was inevitable.