Karma is an MVC framework for Unity3D. Because of how Unity is structured, it actually turns out to be an MVCP architecture (Model/View/Controller/Presenter) where the Presenter is a MonoBehaviour that serves as an intermediary between the Controller and the View. You can read more about this in MODEL VIEW CONTROLLER PATTERN FOR UNITY3D USER INTERFACES.
Based on Zenject
It's built on top of Zenject which provides Dependency Injection (DI). DI is mainly used to route the app to the desired view, it also enables us to build composable and testable systems.
Inspired by AngularJS and ASP vNext
Some of the basic constructs and code layout is inspired by other MVC frameworks such as AngularJS and ASP vNext.
Note to Game Developers
Karma uses concepts like views and presenters instead of scenes. The problem with scenes is that they are too heavy weight, there is no good way to communicate between them, changing scenes is slow (especially if you are doing UI stuff), and they aren't composable. The "Karmic" way of doing a game would be to store each level/scene in a prefab, treat it as a MVC View, store all your characters/entities in separate prefabs, and get them instantiated onto the level's view through DI.
Simple Routing System
Karma has a built in routing system that enables you to create isolated views/scenes as prefabs and easily switch between them. Using an http-like flow, a presenter can Request the router to render another view.
As Stateless as possible
Karma aims to be as stateless as possible to try to give you the guarantee that if you entered a view once with certain Request parameters and reached a successful state, then you will always reach that same state if you pass the the same parameters. Unity3D doesn't provide by default a best practice changing from a view to another. A common way to do this is to have all possible views instantiated in the scene but only enable the current one, the problem is that you maintain state when reusing Game Objects and often end in bad states because of the many paths you need to account for. Karma keeps things simple and functional by just destroying the current view and instantiates a new next view when changing views.
Message Passing
In Karma state is mainly maintained through message passing, being as true as possible to Go's philosophy:
Don't communicate by sharing memory; share memory by communicating.
The added benefit of this is that views become configurable without depending on local storage or static variables, is in turn is very important to keep a system testable.
Pub/Sub System
All Presenters integrate a pub/sub system that enables the communication between entities on different branches and levels in the dependency hierarchy. It's a simple yet powerful message passing mechanism on channels by topic where any Presenter can subscribe and broadcast. By convention the top level application is used as the main channel.
Folder Structure + Conventions
As many MVC frameworks, Karma tries to keep the developers sane by establishing conventions. Among these conventions are the folder structure, concepts (presenters, controllers, services, etc), code organization, a configuration mechanism (dev, prod, test environments).
Parts
Views
Plain old prefabs
Presenters
Handle the presentation layer
Extend MonoBehaviour
Are tied to a Prefab
Get instantiated on Game Objects
Integrate a Pub/Sub mechanism
Are Transient
Are divided as:
Plain Presenter (Routable)
Elements (Reusable)
Layouts (Provide context)
Controllers
Handle the logic layer
Don't extend MonoBehaviour
Are Transient
Are 100% testable
Are usually coupled to a Presenter
Services
Handle Resources
Should be Stateless
Are Singleton
Usually handle communication with a server on a particular resource, local storage, specialized logic for e.g. handling certain user inputs, etc.
Applications
Handle general configuration
Are Presenters
Contain the current view
Can be nested to create subviews
Router
Belongs to a specific Application
Tells the application which view to render next
Can store request history
Middleware
Each application can configure its one pipeline
Each middleware can modify the Request and Response
Enables to e.g. create an authentication layer separate from the view itself
It's asynchronous so e.g. http requests can be made to the server to get extra information