I would like to have a clearer understanding of the pros and cons of various frameworks of turn composition and action economies. That is, I would like to see the relative benefits and drawbacks of different ways game systems handle answering the question about what actions a character can take in a turn (and how many thereof, or how their efficiency is influenced by their number etc.).
Now, of course the lines between framework will not always be sharp, but I think I can post a (non-exhaustive) list of what seems like some of the common paradigms or families thereof, in the hopes that this will better scope the question. Also please note that for the sake of maintaining focus and preventing tangents, I’m not asking about systems of initiative (who goes first), nor about comparing systems with vs. without a way of increasing the number of allowed actions above the default.
Freeform Composition / Build Your Own Turn
Games which give the players the basic ground rules for deciding which actions to fit into a turn, each turn. Often defence and movement are treated just as any other action you can take. Examples would be older books in the Storyteller / Classic World of Darkness (e.g. VtM 2e), where you can Split your dice pool into as many actions as you need and can afford to (e.g. into three actions for performing two swings of your tyre iron [attack] and one dodge [defence]), or Fallout PnP (where you get an allotment of Action Points, and actions cost some number thereof, and one AP is also the cost of moving 1m or boosting defence by a certain value, though ‘default’ defences are free).
This framework seems to be equally capable of supporting the assumption that everyone gets defences for free and the assumption that defences are actions like any other.
Type-Specific Action Slots
Games where a turn usually consists of a certain number (either fixed or upgradeable) of ‘slots’ of specific types, e.g. one move action, one ‘do your thing’ action that can be used for a variety of things (attack, move again, do a noncombat action etc.), and one or two reflex actions (often used for defences if the system puts a limit on the number of defences). Sometimes a systems allows choosing between several different sets of slots. Examples would be Dark Heresy and Eclipse Phase.
This framework also seems to be equally capable of supporting the assumption that everyone gets defences for free and the assumption that defences are actions like any other.
Turn Structure Templates
Games where a player chooses one of a limited, often rather specific sets of actions for a turn, often with specific modifiers baked in. My go-to example would be GURPS, where you can choose e.g. Move and Attack (full movement, poor attack, slightly compromised defence), Move (full move, no attack), Attack (single step move, normal defence, normal attack), All-Out Attack (half of maximum move, attack with a bonus of choice, no defence at all), Committed Attack (attack with a modest bonus, seriously compromised defence, one- or two-step movement), Ready (get a special non-attack action, no attack, one step of movement, and normal defence), and some others.
This framework seems imply a strict regulation of what defences a given turn action structure template includes, and I think it predisposes one to lean towards having a ‘with defences’ structure as the more default one.
I’m sure there are other framework that are distinct from the above three, but I’m currently not able to think of an example I’m well-acquainted with nor a generalised description. A comparison of any such additional frameworks is also welcome if someone is open to including them in an analysis.