Thinking the Unthinkable: Class-free, Level-free D&D?

A disclaimer.

I really don't think this will fly. 

Not that it's impossible to write such a system for an FRPG, RuneQuest did it, Warhammer kind of did it, GURPS Fantasy (and others) certainly did it. So you can certainly write coherent and successful FRPG systems that don't have character classes and don't have levels. 

However, would they be D&D? If you think of D&D, what do you think of? If you're of a certain age, you might think of the satanic panic. Or the cartoon show. But typically you think of a party with a fighter type, a thief type (now reframed as a rogue), a divine caster type and an arcane caster type. If you're a bit less informed you go fighter, thief, cleric and wizard, a bit more informed you might say something like well it could be paladin, monk, druid and sorcerer instead, but you still think of those four roles. If you've played 5e, you might erase the cleric for a bard or a second combat character, and call them by their subclasses, and say battle master, mastermind, hexblade, divine soul say. But that idea of class is integral to how you describe the characters.

An Alternative

I've already described a process in which the characters get a really stripped-down character class, with minimal features, building up their functions a bit from subclasses which open up some invocation choices, but largely from invocations and feats. Lets call the invocations "life chances" for the rest of this post.

What happens if we strip that back a little further? Here is an enormous pool of life chances and feats, some are restricted by prerequisites of other invocations or feats - you have to take the martial weapons life chance to be able to access the polearms mastery feat say, or the extra attack +1 life chance. You need the extra attack +1 life chance and 20 Str or Dex to get the extra attack +2 life chance. And so on.

You still get your archetypal characters: 

• A pure fighter takes all the pure combat life chances. 
• A monk type takes the unarmed/martial arts life chances. 
• A ranger type takes the bow or 2WF combat and then some pet life chances or some sneaky ones or whatever and adds some some nature magic ones. 
• You don't build a Moon Druid or a Land Druid or a Dreams Druid any longer, you choose whether to max out the shapeshifting life chances, the ties to the land life chances or the casting life chances. 
• You build a wizard with your magic life chances, but you can build a bladesinger (or a hexblade) by mixing up your combat life chances with your casting life chances. 

If you go down this route, one feature of a lot of the games I've listed above is that they're also level free. That's not the same as advancement free. 

Buy Packages with XP

One approach is XP per session (like D&D) and you price each package, maybe a flat price, maybe a variable price. So, for example you could have life chances cost 250 xp (and keep xp something like they are in 5e) or make them 50 xp and say you get 10-15 per session on average, so you're saving up for a few sessions. Or you could have variable pricing, so Simple Combat costs 20 xp, Martial Combat costs 50 xp, Unarmed Combat costs 30 xp. This gives you another tool to balance the character development. On that sort of scale, +1 to a stat costs xp=current stat value. 

This approach can seem weird, very weird, to someone who has only played D&D. You can easily create unusual seeming hybrids. For example, lets say you build a fighter who, instead of paying for the next fighter life chance, picks the Healing Magic-1 life chance. They don't look much like a 5e paladin, they don't smite, they don't have an oath, they don't have protection and so on. They look most like a 3rd level Eldritch Knight in fact, but... it's divine magic rather than arcane. And, rather than picking any more, they go back to just "fighter" life chances thereafter. But if someone in the front line goes down, they can shoot out a healing word. Nice.

Use It or Lose It

Another approach, used in RQ and a few other games, is "advance what you use". So if you use a given skill in a stressful situation, you tick it. During downtime - which really has to be worked into the game - you get a chance to improve the skills you ticked. RQ makes magic an integral part of every character, wizards are, typically, a meaningless class. But you could make casting each spell a skill (you would probably want to do away with saving throws or at least drastically alter them, and totally rewrite save or suck spells if there's a chance for all spells they just don't work). If you make magic skill-based in 6e, something I am certainly not opposed to, I would still keep the MP system I outlined earlier, but make each spell a single action, and adopt the 3 actions in your turn rule, so a caster can try to cast up to 3 times. There might have to be a rule about the maximum number of MP you can spend in a single round so a high level caster, or rather one with good skills, doesn't just go maximised fireball, maximised fireball, maximised fireball as their three actions, but I think that's achievable.

In this approach, however you handle magic, the same fighter type can still pick up the Healing Magic-I life chance, but if they don't cast their Cure Wounds and Healing Word equivalents, they won't be very helpful come the time a colleague goes down. Of course, if you take this approach, you might move away from the life chances paradigm altogether. Under this approach, anyone can learn any skill, within reason, and the fighter just spends time and money learning the Cure Wounds skill, regularly uses on themselves and the people standing next to them in the front line and advances it as regularly as their weapon skills. Magic Weapon, which would be a Transmutation-1 spell (it's only second level after all) so why not pick that up too? This is where I think completely moving away from the life chances model breaks down. I have no issue with the fighter character picking the Transmutation-I  and Healing Magic-I life chances and giving up something else, or delaying them at least. But everyone having access to most/all skills requires an additional framework to make it work nicely. In RQ that was present - everyone joined a cult (this was basically a religion) and to advance in the cult you had to meet certain skill and state requirements and, usually, behavioural requirements: the cults were a religion after all. Humakt was the God of Death and Honour (Truth), hated undead, liked honour duels and so forth, loved swords. You needed 5 skills from his approved list, at least three of which had to be straight-edged "sword" combat skills (thrown dagger and dagger counted, cutlass didn't). Thanatar, a very different God (actually three, who worked together as a single entity) shared the Death and Truth runes (but expressed Truth as Knowledge) and added Darkness and Chaos. Worshippers of Thanatar used to headhunt people, literally, chopping off their heads with a garrotte, using evil magic to trap their spirit in the head and casting the spells the head knew from it. To advance in this cult, you need stealth skills, garrotte and I think short sword. So your differences came from the cult you joined. I don't think D&D needs that, I think the reworked invocations as life chances can provide the same thing, even in a "use it to improve it" system.