I'm curious to see if there's a game out there that implements an active time battle system similar to Final Fantasy VII or Chrono Trigger, only with fully asynchronous combat.

The main limit (and problem) with traditional active time battle systems is how they only process 1 combat action at a time. This means if there are a lot of things on the battlefield, combat becomes incredibly slow as anyone taking any action pauses the game for everyone else.

The obvious solution is to have all combat actions happen at the same time. Consider a modified active time battle system where all characters can act immediately when ready, no matter what else is happening. If half of the characters on screen are clashing when it's your turn, feel free to jump right in. When a player character is ready (the timer gauge fills up), a menu appears (or the controls become available on whatever control scheme you're using, doesn't have to be a console-style JRPG) and whatever command the player issues occurs immediately on selection.

A fully asynchronous active time battle system could implement the traditional active/wait choice. Active means everything happens in real time and shuffling through command menus or fumbling with the controls costs you turns versus everything else. Wait means that time pauses when at least one player character can take an action, and there would be some additional control you can hold down to continue while taking no action (usually to wait out temporary retaliation buffs). You could also have a difficulty meter attached to the active time battle system where maximum difficulty means the AI "instantly" makes its move whenever available and lower difficulties have the computer simulate shuffling through menus or controls with varying levels of skill (effectively decreasing the rate at which NPCs act).

The answer to this question doesn't have to be a JRPG or console-style RPG, although I would strongly guess that most of the answers (if they exist) will be JRPGs.

Final Fantasy IV?

I feel like doing that would be impossible. Any ATB game where a party's members can do actions at the same time would have to have either the following: AI controlled party members or a pause after each attack where you decide what attacks your team will use. Both of which wouldn't make the game 'ATB' anymore.

The other problem with this is games that use an ATB system, often have very impressive looking attacks (Think Final Fantasy's magic or summons), if 3 of these were going on at the same time it would look like a mess.

Of course technically you can just wait for all party members to 'ready' themselves and quickly choose there actions so they all perform their attacks in a row.

Final Fantasy X-2 might be what you're looking for. Also, though not pure ATB (there's positioning involved), my understanding is that the most recent versions of Final Fantasy XII allow multiple simultaneous spells.

By the way, there is one issue that I can see with your idea; race conditions. What happens, for example, if the character dies in the middle of performing an action, or has all MP drained (or gets silenced) in the middle of casting a spell?

Incidentally, there are differences in the ATB systems of the Final Fantasy games. From what I remember:
FF4 (2D): Time stops during attacks. Also, at least in WSC and GBA 1.0 (maybe in the original?), there's no queue; if multiple characters are ready to act, there is a specific priority order (for example, the party member in the middle gets priority over the rest of the party); this can result in characters being starved of turns.
FF4 (3D): Time stops during party member attacks, but does not stop during enemy attacks. (Yes, this is asymmetric; I think this mechanic ends up favoring the player, especially when combining Berserk and Hastemarch.)
FF5: Time stops during attacks. Unlike some versions of FF4, there is a queue, causing actions to be resolved in the order they come in. One interesting feature (that was removed in the phone versions from what I can tell) is that, when a party member gets a chance to enter a command, time briefly stops for an amount of time dependent on the battle speed (and that's the only effect of battle speed).
FF6: Time does not stop during attacks. There is a queue, which can become quite large if another charater's ATB fills during a character's action. (If the battle mode is set to Wait, opening a submenu (like Item or Magic) will stop time, but actions that are already in the queue will get executed. (I have found myself having to do this a lot, and found this to be the main issue with FF6's and FF9's ATB.) Regen and Sap can trigger during actions, but will only be applied after the action resolves (and each character can only have one pending Regen or Sap event at a time).
FF7: If set to Active or Recommended, time doesn't stop during most actions; if set to Wait, it does. Time *always* stops during summon animations (which is a good thing, as they can get rather long). Annoyingly, however, targets can't be selected for actions during summon animations.
FF8: Time stops during all actions, just like in FF4 or FF5.
FF9: Time does not stop during actions, just like in FF6. Unlike FF6, Regen can trigger during actions, and summons can have long animations, leading to silly situations in some cases. For example, by the time a long summon animation finishes, the party may have been fully healed by Auto-Regen, and the Shell spell that the enemy had cast may have worn off, causing it to not provide protection.

Not sure if that's what you mean, but you could check out "The Spirit Engine 2". (Google it, it's free both in terms of money and DRM).

You have 3 characters that charge up their spells, you can have them release the spells as they are ready or pause and release them manually. Pausing them longer also results in a stronger spell. Each character uses their spells independently. For example, you can tell your party to all pause for a moment and wait until an enemy charges for a melee attack and then release all at once to take him out. Or save up energy and react to an enemy spell, like giving yourself a magic shield if a big magic attack is coming your way and so on. There's also a multihit multiplier where hitting an enemy often in a short timeframe increases all damage, so timing is important.

The game has 3 different speeds and a pause button. As for spells, you can change the current spell for any of your characters on the fly or build some chains that they go through automatically (you can even make entire party chains), though I personally didn't find that necessary and liked to have complete control during combat.

Your party is lined up and so is the enemy, you can (and have to in most cases) shift your lineup constantly to bring someone else to the front to tank while others go to the back. Since melee attacks force a character to run to the enemy and some spells have effects like doing more damage the more enemies they pass through or hitting specific enemies and ignoring the frontcharacter timing and positioning is again very important.

The game is very linear and not voiced, but has nice art and a great soundtrack (around 100 different tracks iirc, it's all uploaded on youtube). It also has some nice replay value since different characters have their own sidestories, and certain characters have different dialogue depending on party members.

Also, the first "The Spirit Engine" is worse in pretty much every regard and also plays differently (worse) in my opinion, and the 2 stories are basically completely unrelated, so if you decide to give it a try I'd really suggest ignoring the first one and only playing the second.

Western "AAA" production-grade games have more impressive visuals going on at the same time and have no problems keeping it all together. Wrong. There are extremely easy ways to prevent race conditions simply through prioritization rules.
In fact, if race conditions are happening, the devs must be comically incompetent.

First, I'll start by saying fully asynchronous ATB is a mechanical proper subset of full real-time (a lot of games out there, including RTS, MOBAs, battle royale, FPS, action-adventure, many western RPGs, ...), and also real-time with pause ("Bioware games").

With that being said, every other genre seems to handle fully asynchronous real-time combat just fine with no race conditions.

Video games generally run in a controlled infinite loop. Sometimes, each run of the loop implements a frame. Alternately, loops could run faster than the framerate, with additional factors controlling which runs of the loop produce a frame.

Consider fully asynchronous ATB where every action is pegged to a frame. Then you can have an "interrupt loses" rule where:
* If a character using an ability gets mana-drained below cost in the same frame the ability is used, the ability takes precedence and the mana drain is applied on whatever is left over.
* Interrupts are processed before characters start using their abilities in any given frame. If a character gets interrupted on the same frame that a cast or other ability starts, the interrupt doesn't happen. (If the interrupt was a frame later it would be a different thing entirely.)
* In any frame, characters record the damage and other offensive effects they would apply before taking any damage. Therefore, if 2 characters hit each other with unmitigated fatal damage on the same frame, both die.

Hmmm....

I can't help but recall and enjoying FF12, where the Gambits allowed you to basically write an AI, specifying priorities, who to attack/heal when and how. And a few for out of combat when there's no enemies what things to do. Honestly not enough Gambit slots to fully do them, but you could assign different tasks to different characters. You could also pause the game to do specific actions like healing a party member overriding the AI for a short time.

I want more programming fighting game combos...

Wow, talk about a blast from the past. I remember playing the original, and hanging around the same Indie dev sites as the game's creator, back in the day. I didn't know about the sequel, or at least forgot about it after all these years. Now that it's freeware, I'll give it a try, and most likely will donate some money to the dev.

Thanks for mentioning the game!

By the way, here's the official website, for anyone who'd like to check it out: http://thespiritengine.com/tse2-info.html

Only thing is that actions generally take more than one frame to complete, as the game still has to show animations. What happens if a spellcaster gets reduced to 0 HP during the animation of a Drain spell, for example? (Will the caster be alive when all is said and done?) What if the target gets killed (or, in the case of resurrection effects, revived) during the animation?

You can't just peg every action to a frame unless you are willing to lose the animations, or otherwise have things look strange.

As a specific example, Final Fantasy 6 has such a condition involving the Slot effect Joker Doom; if the user is inflected and cured of confusion before the party-targeted version is cast, the spell will affect the enemies instead, which is a major (though sometimes tricky to pull off) exploit (instant death to all enemies that always works and ignores immunity).

Isn't this how RTS games work?