Non-Linux FOSS: Install Windows? Yeah, Open Source Can Do That.
For my day job, I occasionally have to demonstrate concepts in a Windows environment. The most time-consuming part of the process is almost always the installation. Don't get me wrong; Linux takes a long time to install, but in order to set up a multi-system lab of Windows computers, it can take days!
Thankfully, the folks over at https://automatedlab.codeplex.com have created an open-source program that automatically will set up an entire lab of servers, including domain controllers, user accounts, trust relationships and all the other Windows things I tend to forget after going through the process manually. Because it's script-based, there are lots of pre-configured lab options ready to click and install. Whether you need a simple two-server lab or a complex farm with redundant domain controllers, Automated Lab can do the heavy lifting.
Although the tool is open source, the Microsoft licenses are not. You need to have the installation keys and ISO files in place before you can build the labs. Still, the amount of time and headaches you can save with Automated Lab makes it well worth the download and configuration, especially if you need to build test labs on a regular basis.