Speed

Sonic was built to be fast. Every core architecture decision was benchmarked to determine the fastest possible solution.

It is far from a perfect science, but in simple Apache benchmark tests Sonic is ~800% faster than Zend Framework.

View the benchmarks.
Simplicity

The code is clean and easy to follow. You can search, but there is not a single else statement anywhere to be found.

Getting started is as easy as running an installation script, adding a vhost, and hitting your page in a browser.

Create a project.
Power

Sonic is designed to be extremely scalable. There are many extensions available to extend the core functionality.

The ORM module, for example, allows you to sync model changes to your database without having to write any SQL.

Browse the extension gallery.

Key Features

Turbo Mode

Sonic has an implementation of Facebook's Big Pipe built right in. You can easily toggle in and out of turbo mode, and it automatically handles users and search engine crawlers that don't have JavaScript enabled.

View source on this site to see what it looks like.
Application Delegation

Sonic let's you specify an App Delegate that will receive messages when events occur in the application such as when an action runs or when a view is rendered. This allows you to easily extend the functionality of Sonic without touching the Application class.
Multilevel Views

Sonic supports rendering any controller/view combination from within any other view. This can go infinite levels deep and makes ajax calls really easy.

New in 1.1

Version 1.1 is the biggest release of Sonic since the initial launch in late September 2010. It brings with it a ton of improvements, bug fixes, and new features.

The core idea of Sonic from the beginning was to build a light framework. Most frameworks begin to get cluttered as new features are added. In this release a lot of code has actually been removed including the cache, database, and ORM modules. Don't worry though, they are not gone forever. They have just been transformed into extensions.

Official extensions are stored in a remote repository so it's really simple to install and upgrade extensions. This also means extensions can be upgraded outside of the core framework.

Check getting started with extensions for more information/help working with extensions

Other updates in version 1.1 include:

improved templating
improved routing
improved config handling
numerous bugfixes