On the Acquia blog there's a new post looking at the evolution of the PHP language and some of the newer features included in recent releases.

PHP is not a young language. As of 2013, it's 18 years old; that's old enough to vote. Many upstart languages have appeared over the years to try and unseat PHP as the "lingua franca" of web applications but it still commands over 80% of the web market. One reason for PHP's popularity is no doubt the ease with which new developers can get started with it, but just as important is the fact that PHP has been evolving for all those 18 years.

He covers things added over the last several major revisions of the language (with code examples) - things like anonymous functions, traits and generators.