Ember.js is an open-source JavaScript web framework, primarily used for creating single-page web applications (SPAs). It's built on the principle of convention over configuration, meaning it provides a set of sensible defaults that help developers build modern web applications more efficiently. These defaults enforce best practices and encourage consistency across the codebase.

Ember is often compared to frameworks like React or Angular, but there are some differences. For instance, Ember comes with its own integrated development toolset, Ember CLI, which provides a standard application structure and build pipeline.

Here are some key concepts and features in Ember.js:

Routes and Templates: Ember.js uses a routing system to manage application states. For each route, you can define a corresponding template which is used to render HTML.
Components: Like many modern frameworks, Ember.js emphasizes component-based architecture. Components in Ember are reusable pieces of code that can manage their own behavior and maintain their own state.
Services: Services in Ember.js are singleton objects that can be accessed from any part of the application. They can be used to share and maintain state across different parts of the application.
Data Layer (Ember Data): Ember Data is a library included with Ember.js for handling models and relationships, as well as loading and saving records. It provides a consistent interface to interact with different types of APIs.
Handlebars Templating: Ember.js uses the Handlebars templating engine for its views. This allows for clear and expressive templates.
Autotracking and Glimmer Components: Introduced in more recent versions of Ember, the autotracking system automatically tracks dependencies and re-renders components when their state changes. Glimmer components are a lightweight, more performant iteration of Ember components.
Testing (test-driven development): Ember has strong testing tools built-in, supporting different types of tests including unit, integration, and acceptance tests.

Ember.js (open source javascript framework) is suitable for building large-scale, complex applications, due to its full-featured nature and emphasis on convention.

When looking to hire Ember js developers, there are several options available. You can browse online directories like Clutch or Goodfirms, attend events and conferences to meet developers in person or search the internet for Ember development companies. It's important to carefully review the company's portfolio, read their blog, and check testimonials from previous clients to assess their experience, expertise, and customer satisfaction. This will help you make an informed decision when selecting a js Ember development partner.

When hiring an Ember js developer, it's important to assess their skills and expertise. Here are three key skills to look for:

Proficiency in JavaScript: Ember.js is built on JavaScript frameworks, so strong proficiency in the language is essential. Look for developers who have a solid understanding of JavaScript concepts, including ES6 features, closures, scope, and asynchronous programming.
Ember.js framework knowledge: Ensure that candidates have a deep understanding of Ember.js and its core concepts. They should be familiar with Ember.js conventions, such as components, templates, routes, and services. Experience with Ember.js add-ons and ecosystem tools is also valuable.
Problem-solving and debugging abilities: Effective Ember.js developers possess strong problem-solving and debugging skills. They should be able to analyze complex issues, identify bugs, and implement effective solutions. Look for candidates who have experience troubleshooting Ember.js applications and can demonstrate their problem-solving abilities.

Ember.js, a JavaScript framework for building web applications, supports Agile development methodologies in various ways:

Convention Over Configuration: Ember.js follows a "Convention over Configuration" principle, which means that it provides developers with the best practices and conventions to follow. This helps speed up the development process by minimizing the need for decisions that can slow down Agile teams.
Integrated Testing: Ember.js has built-in testing tools that support Test-Driven Development (TDD), a popular practice in Agile. This enables developers to write tests first, ensuring the functionality before the implementation, thereby reducing the chance of introducing bugs into the system.
Component-based Architecture: Ember.js uses a component-based architecture, which promotes the division of work into small, manageable tasks. This aligns perfectly with Agile methodologies that encourage incremental and iterative development.
Detailed Documentation: Ember.js has a rich set of documentation which allows new team members to quickly get up to speed, ensuring that the team's velocity is maintained even when the team changes.
Data Binding: Ember.js' two-way data binding simplifies the handling of user input, which can speed up the development of user interface functionality.
Ember CLI: Ember Command Line Interface (CLI) is a powerful tool that can generate boilerplate code for you. It improves development speed and encourages the DRY (Don't Repeat Yourself) principle.
Hot Reloading: Ember CLI supports hot reloading which immediately reflects the changes in the codebase on the web page. This helps in getting instant feedback during development, a key aspect of Agile methodology.
Community and Add-ons: Ember.js has a vibrant community and a multitude of add-ons, which allows developers to extend the functionalities of Ember applications without having to write everything from scratch.
Routing: Ember.js' routing is focused on the URL, this makes it easy to build multi-page, bookmarkable web applications. This can speed up development and help teams deliver user-valued functionality more quickly.
Ember Inspector: Ember Inspector is a browser plugin that makes debugging Ember.js applications easier. It helps developers identify and fix issues more quickly, thereby reducing time spent on bug fixing.

These features facilitate a rapid, iterative approach to development, which is a key tenet of Agile methodology.