When it comes to simplifying web application development, Ruby on Rails gems are invaluable tools that can help streamline your workflow and enhance your app's functionality. Here are the top 5 Rails gems that every developer should consider integrating into their projects:

1. Devise: This gem simplifies user registration and authentication, offering customizable modules for everything from password recovery to account locking.
2. ActiveAdmin: A powerful administration framework that provides a clean interface for managing your application's data effortlessly.
3. Pundit: This elegant gem offers a simple way to manage user permissions and access control, ensuring that your application is secure.
4. Paperclip: Facilitate file uploads in your Rails app with ease, handling image uploads and attachments seamlessly.
5. Sidekiq: A background job processing gem that allows you to run tasks asynchronously, improving your app's performance and user experience.

Convention over Configuration is a key principle in Ruby on Rails that significantly simplifies the development process. This paradigm encourages developers to follow established conventions rather than spending time configuring details extensively. By adhering to these conventions, developers can enjoy reduced decision fatigue, leading to faster project setups and streamlined workflows. For instance, when naming files and classes according to Rails conventions, the framework automatically understands the relationships and behaviors, allowing developers to focus more on building features rather than wrestling with configuration files.

This principle not only enhances productivity but also promotes a standardized way of writing code. As a result, teams can collaborate more effectively, as anyone familiar with Rails can easily jump into a project regardless of its specific configuration. Moreover, the Rails community supports this methodology with rich documentation and resources that align with the conventions. By embracing Convention over Configuration, developers can unleash their creativity and innovate without getting bogged down by the minutiae of setup, making it a true game changer in the world of web development.

Optimizing your Rails app for speed and performance is crucial for enhancing user experience and improving your site's search engine rankings. Start by minimizing asset pipeline loading times. This can be achieved by compressing JavaScript and CSS files, as well as using tools like Webpack or Sprockets to manage and serve your assets more efficiently. Additionally, consider implementing HTTP/2 to allow multiplexing of requests, further reducing the loading time of your assets.

Another essential aspect of performance optimization is database management. Utilize database indexing to speed up query execution times, and avoid N+1 query problems by using techniques such as eager loading. Regularly analyze your database queries with tools like the Rails performance gem to identify bottlenecks and optimize them. By focusing on these practices, you can significantly enhance the speed and performance of your Rails application.