Я писал такой концепт диалоговой системы для одного джема.

Thing I'm researching with this is a system of conversation with NPC that is based not on usual dialogue tree or puzzles (like in Oblivion), but on player's experiences.

Player collects experiences on the course of playing, and then discusses them with NPCs for fun, but mostly for profit.

First, what is an experience? Simply put, pretty much anything. If it can be "achievement" in game-mechanic therms, it can be an experience. Also, experiences examples are:

Visiting some place
Killing an enemy
Using a skill
Finding a (preferably interesting) item. Or even just having it or looking at it.
Advancing a quest
Talking with someone
Hearing or reading about someone or something
Learning some fact from observation, talking or reading a document

Then, when you have a library of experiences (kind of like an inventory, but with bits of information, instead of items), you can use them to try to "talk about <this experience>" with NPCs

What can you get out of that depends on the experience in question, and, of cause, who are you and the person you are talking are.

If the theme is interesting to NPC, he/she will more inclined to continue talking.
Or he can be bored, if it's something trivial and/or out of his sphere of interests.
She can give you some advices on the matter, raising your skill level.
He can like you more or less, if you tell about some (according to him) good/bad thing you have done
She can tell some fact that can be used as an experience when talking with someone else.
He can ask you for some relevant service or item. Give you a quest, or just ask to give/sell an item you have told about.
She can offer you relevant item/question. Such as if you show her your ruined sword, she can offer you to repair it or give/sell you a better one.

Now, how do we know which reaction will you get?

It depends, mainly, on two things - who you are talking with, and how interesting/new/unique your experience is.

For example, let's say you have killed a dragon with a magic sword, and collected it's hoard. It breaks apart into several experiences, which will be interesting to different people:

"I have found a dragon's cave" - tell that to a ranger or traveller.
"I have observed a dragon" - mage or a scientist will be interested in your observations.
"I have fought a powerful enemy" - talk about that with a warrior.
"I have fought using a magic sword" - talk with a smith, he can be interested to hear about exceptional weapons and the way they are used. Maybe he'll give you some tips about how to care about your swords.
"I have killed a dragon" - any people that were attacked by this dragon before (such as local peasants) will be happy to hear about it.
"I have looted a dragon's hoard" - merchants will be interested to offer you some options to sell something you have found, or offer you some way to spend the money.
"I have found an artefact (in the dragon's hoard)" - again, tell mages or merchants about it.

Even if the game knows only the basics about NPC - such as class/profession, level and location - it can generate appropriate reaction. Such as, Peasant class NPC that lives in a vicinity of dragon's cave will likely to know and hate the dragon, and thank you for killing him. High-level characters (VIPs) that live in same town are likely to know and be able to tell something about each other, and be interesting to hear some news about each other.

In addition to that, NPC can have some semi-hidden character traits, which can be hand-picked or randomized (or both). For example "pacifist" character will not be interested, or even appalled to hear about fights and weapons, "talkative" will like to speak about everything more, etc.

Ideally, but not necessarily, NPC could have a dynamic life of themselves, gaining their own memories that they can tell/be asked about. There are already many games that do that: Mount&Blade, Crusader Kings, Tropico, Dwarf Fortress, Rimworld, Space Rangers etc.