2.0 Updated test conversion Starfinder >> 3 action economy
Everyone gets 3 actions in their turn. Enemies too of course.
The keyword or tag system is amazing and would need to be implemented in order to define what an "attack", or a "move" etc. is.
1. ATTACKS = a single attack is now a 1 action activity. Attacks after the first, during your turn, suffer a penalty: "M.A.P." 0/-5/-10 (0/-4/-8 for operative weapons)
2. COMBAT MANEUVERS are considered attacks for the purpose of the MAP
3. FULL ATTACK does not exist anymore. As a general rule, substitute every "full attack" equivalent action into a 2 action activity that is always considered as counting for 2 attacks for the purposes of the MAP (see above)
4. STANDARD ACTION = 2 action activity (single attacks are now 1 action activities)
5. MOVE ACTION = 1 action
6. SWIFT ACTION = 1 action, but should normally only be allowed once per turn, unless specified otherwise.
7. REACTION = stays the same.
8. FREE ACTION = stays a free action
9. SPELLS = casting time now goes according to points 4, 5 and 6. Every spell that involves an attack counts for the purposes of MAP
10. FULL ACTION = does not exist anymore. Easier to adjust case by case, with the principle of: should become a 2 action activity that generally would not allow for the 3rd action to be used for an attack action.
11. MOVEMENT SPEED: 5 ft less for everybody. Wherever says 30 ft, in terms of the basic movement speed of a creature, it's now 25. If it was 20, is now 15. Same for every basic movement that a creature has (e.g.: fly 60, now becomes fly 55).
FEATS that allow attacking and moving freely: such as Spring Attack and Shot on The Run are no longer useful. However, they could be replaced by 1 feat that improves the effects of Mobility, giving more resources to deal with AOOs (such as, make an enemy re-roll their AOO, or things of this nature)
AUTOMATIC FIRE: the penalty for all the attacks is now -4 (same as it was before when we had the full attack). Everything else stays the same, only difference: you don't consume your entire magazine, the ammo used is still double the normal amount for each target, but nothing more. (sorry I had to add that, I hate how it currently is!)
UNWIELDY: these weapons take 2 actions to attack with, and they count as 2 attacks for the purposes of MAP. Everything else stays the same (you still can't make AOOs with them)
BLAST: every attack with a blast weapon has an additional -2 to the attack roll (same as before). However, blast weapons can never be fired more than twice per turn. Everything else stays the same
MULTI-WEAPON FIGHTING: your multiple attack penality is now 0/-4/-8 with small arms. Your operative weapons now have 0/-3/-6 multiple attack penalty. This affects the triple/quad attack ability: your penalty is now -3 for all three/four attacks, in that case
MULTIATTACK for monsters: now a 2 action activity, but all attacks are done at -6.
TRICK ATTACK: stays the same (you can move and attack with this new 2 action activity), but it counts as 2 attacks for the purposes of multiple attack penalty. Furthermore, the enemy stays flat-footed for rest of your turn even in the basic version of trick attack (allowing you to use the 3rd action to attack again, with a -10 or -8 as per the general rule).
TRIPLE/QUAD ATTACKS: they are 2 action activities that let you make 3 and 4 attacks, respectively. In both cases the penalty is -4 for all three or four attacks. In a turn where you used these abilities you cannot use your 3rd action to attack (or you cannot perform Triple/Quad attack if you have already attacked once during this turn).
HASTE Spell: you can now move up to your speed during any 2 action activity (before and after the activity if you want), for free. The rest stays the same.
FEATS/ABILITIES that convert move to switf actions: in this case, generally the swift action could be turned into a FREE action, but make it so it can't be done more than once per turn.
CHARGE: is now a 2 action activity. So you can move up to double your movement and 1 attack with the listed penalties, within this activity. However, if you then don't take any other attack action, or you don't move anymore (move-equivalent actions such as making a skill roll don't count), you can wave the -2 AC penalty. Otherwise, it applies as before.
E.g. you could move, then charge (which will effectively let you start the charge from the angle you want), in this case you will end up having the -2 to CA penalty as well.
COUP DE GRACE: is now a 3 action activity. Everything else stays the same
FIGHT DEFENSIVELY: is now a 3 action activity that lets you trade one of the actions for a guarded step at any time during the activity. If you attack, the penalty for each attack (1, 2 or 3) is -8. Everything else stays the same
TOTAL DEFENSE: is now a 2 action activity. Same restrictions apply. Furthermore, you cannot take any attack action in a ROUND where you used this activity (this includes combat maneuvers, of course), cast any spells or use any spell-like or special ability. You can only use your remaining action to move or to take a guarded step.
RUN: is now a 3 action activity, where you can only move up to four times your speed with all the same restrictions as before.
WITHDRAW: is now a 3 action activity. Everything else stays the same