PHP stands out because it is one of the first languages built for Web. No wonder it offers an alternative syntax that is more usable as a template language instead of a programming language. They help us avoid the block-kind code and have single-line PHP code. It is also simple enough for a designer to pick it up.
There are of course many template engines offered for PHP, like Smarty and PHPTAL. However, they might turn out to be heavy for many projects. In such cases, using the alternative syntax can help a lot. A couple of popular tools are WordPress and CodeIgniter.
Of course, one of the dangers of using PHP directly in templates is to make it one-stop for everything. The fact that PHP has two different syntax forms should encourage us to think about separating what to allow in templates, which can be a challenge in itself if not consciously designed.