This puts me in mind of Jeff Vogel's CRPGs published through Spiderweb Software: Avernum (used to be Exile), Geneforge, For the Queen etc.Some examples: Most PCs have between 6 and 10 AP, depending on class and level. Doing anything costs an AP, such as:
- Most medium-sized humanoids can move 15 feet per AP spent (smaller sized might have a rate of 10 feet, while something like a horse might have 30).*
- Attacking with light-rated weapons costs 3, medium 4, and heavy weapons 5*
- Spells costs between 3 and 6, depending on complexity
- Dodging costs 5
- Disengaging costs 4
- Disarming a trap costs 6
- Drinking a potion costs 4
- Using a response (like reaction in 5e) costs 1 or 2 if you have them available
* This varies, as there are class abilities you can take to increase movement or reduce the weapon cost (like the swashbuckler specialty)
Desperation actions are:
- Damage Resistance: Gain Damage Reduction of 2 points until the end of your next turn.
- Burst: Increase your movement rate by 20 feet until the end of your next turn.
- Focus: Gain a bonus die level equal to your Chapter level+1 when you attempt any Challenge roll.
- Recovery: End a negative status on you.
- Arcane Boost: Spells cost 1 spell point per your Chapter level less than normal until the end of your next turn.
- Desperate Strike: Gain a bonus WD per your Chapter level. Apply this as bonus damage to an attack roll you have successfully landed. Use this trait after landing the attack.
So desperation points are much more impactful than a single or two loss of AP. They are to represent that "the fight is going really hard, you’re beaten down, and in desperation, you are able to tap into resources to achieve extraordinary tasks."
They all use a very similar action point system, with the caveat that you can take any action as long as you have 1 AP left, your turn will just end thereafter if it would take you over the maximum. They also had some interesting incentives, where items tended to be lower power than spells/abilities, but took only 2-3 AP to use, so working a wand/potion into your combat routine made a lot of sense. Those games use a point buy system with some primary attributes that serve as prerequisites and provide increasingly inefficient scaling to a large quantity of skills, and the skill that ups your action points is usually in high demand. They also did stuff like offering a chance to swing more than once once when you attacked, or items that occasionally made an action not take points or messing with the point efficiency of specific actions/movement and so on.