It hasn't actually done anything. It's an installer file for PEAR, which is a set of PHP frameworks.
In case that doesn't sound like English, here's the quick and dirty rundown:
PHP is a programming language. It's used almost exclusively for writing programs that run on a Web site. For example, WordPress, the popular blogging program, is written in PHP.
Mac OS X is more than just a desktop operating system. It comes with Web and file serving programs as well. The Web server built into every version of OS X is a full-featured, powerful Web server package identical to what powers most of the world's Web sites. In addition to serving up Web pages, your Mac comes equipped to run Web programs like WordPress or Joomla or Drupal or zillions of others, because it includes PHP (along with other Web languages like Ruby, Python, Perl, and so on). Essentially, though it's turned off by default, your Mac is a full, powerful Web server and application platform; you could turn on the Web server, stick your Mac in a rack at a datacenter, and it would fit right in alongside all the other Web servers there.
Programming in PHP is a bit annoying in the sense that most of the time, if there's something you need to do, you need to write all the code to do it yourself. Let's say you want to write a Web site in PHP and you want people to be able to log in. Maybe it's a social networking site you're writing, maybe it's a Facebook clone, maybe it's a blog, maybe it's a dating site, maybe it's a store--but for whatever reason, you need to have people be able to log in. Normally, you'd write all the code for handing creating an account, storing it in a database, keeping track of who is logged in and who is not, and so on, and so on, yourself.
But wait a minute, people have already written this kind of code a zillion times before. WordPress is written in PHP and it has functions to do this. Drupal is written in PHP and it has login functions too.
That's what an "application framework" is. Basically, it's a skeleton for a program. It's a way of saying "A lot of programs for the Web need to be able to do a lot of things in common, like have users log in and out, play sounds, have users create accounts, be able to pull messages or posts from a database, be able to encrypt information to store it safely, be able to send an email, be able to upload or download pictures, and so on." An application framework is basically just a big collection of subroutines to do a lot of common tasks, so that you don't have to.
That's what PEAR is--a huge collection of subroutines for programs written in PHP.
By default, PEAR is not actually installed on your Mac...but the installer file is included on your Mac, so that if you are a PHP programmer, you can just install it and use it without needing to download it from the Internet. The file "install-pear-nozlib.phar" is, like its name suggests, an installer file for the PEAR framework.
Unless you are a PHP programmer *and* you want to use PEAR, this file will sit unneeded and unnoticed on your Mac and you'll never do anything with it.
