The .NET framework was released in 2000 by Microsoft. An open source implementation of the platform, Mono, was the center of controversy in the early 2000s because Microsoft held several patents for .NET technology and could have used those patents to end Mono implementations. Fortunately, in 2014, Microsoft declared that the .NET development platform would be open source under the MIT license from then on, and in 2016, Microsoft purchased Xamarin, the company that produces Mono.
