Back in 2008, Microsoft rolled out the DreamSpark program as a means to get Microsoft software design and development tools in the hands of students at no charge. It was initially only for university or college students, but it has been expanded to also cover high school students. Basically, this means that any high school, college student, or faculty member (in most major countries) can download copies of many Microsoft operating systems, servers, and development tools for free. If you fall into one of those categories, it is pretty easy to get signed up and verified into the program, so you can get your hands on the software for free.
Of course Microsoft is not doing this simply for altruistic reasons. They want more people to be familiar with Microsoft products and technologies, so that they are more likely to use them and recommend them in the future. There is nothing wrong with that, and if you are a student or educator, you might as well take advantage of the program!
Some of the most valuable software-related items are Visual Studio 2013 Professional, Windows Server 2012 R2 Standard, and SQL Server 2014 Developer Edition. You can also get a free 90-day subscription to Pluralsight On-Demand, a number of free eBooks from Microsoft Press, along with discount vouchers for Microsoft Certification exams.
The Microsoft DreamSpark site has more details about the program.