#5 Windows Server 2008 R2:

For years, tech giant Microsoft was keen to enter the server and enterprise sector and in 2008 they launched their first operating system for servers, the Windows Server 2008 R2. Initially Microsoft launched R1, which particularly was a flop. The OS R1 was an operating system based mainly on Windows Vista, which obviously was one big loss in Microsoft history. The second one, the R2 version was based on the latest Windows 7, which was particularly a hit among servers and IT admins and experts.

 The operating system comes up with a number of features like ASP.NET support or capabilities to run Microsoft’s IIS server with the included advanced API. But still with all these features, the Windows Server 2008 R2 has some major drawbacks. The customization part is one main problem, as the OS is not an open source and users have to keep on waiting for support from Microsoft.