According to the Sitepoint poll of PHP programmers we mentioned a few weeks ago, the second-most popular framework after Laravel was Phalcon. This is a fairly remarkable achievement, considering that the framework itself is only about 2 years ago, near the beginning of 2012. As the internet grows by leaps and bounds, and traffic grows right along with it, there's bound to be a greater and greater focus on performance issues, and this where Phalcon really distinguishes itself from more typical PHP frameworks: as its documentation says, "Phalcon is an effort to build the fastest framework for PHP."
So how does it manage this? It's primary advantage comes from the fact that it's entirely C-extension-based. Not a very common strategy among popular PHP frameworks, being coded in C gives Phalcon the majority of its performance advantages. The C extensions are loaded at the beginning of web server's process and then reside in RAM, allowing Phalcon to process over 2300 requests per second, nearly three times as many as CodeIgniter is able to manage. Other than this aspect, however, it operates more or less the same as any other modern MVC-framework for PHP, offering an array of features you've come to expect like object-relational mapping, a query language, a templating engine, and other such goodies. Add in a burgeoning community of other developers working with the language, and you begin to see why Phalcon has quickly risen from relative obscurity to become one of the most appealing frameworks for your upcoming large scale, performance intensive projects.
The success has driven development fairly quickly as well, and Phalcon 2.0 is in the works, with the first alpha version already released. There are a fair number of changes under the hood, which should ease the concerns of some developers who have resisted Phalcon and other C extension frameworks for the simple fact that they don't know C very well and aren't keen to learn. This made it very difficult to do any sort of bug fixing, in the unlikely event that something went wrong. The new version of Phalcon has the majority of its behind-the-scenes processes recoded in a language called Zephir, an open-source language that compiles and runs with a speed similar to C. If you're interested in helping test-drive the alpha version of 2.0, they're always looking for more assistance!