This has been mentioned in a few articles now, however its a pretty big milestone for Microsoft and deserves its own mention in the count down of the year.
Microsoft have said in the past that they have love for linux, however this year they have announced with the new Rosyln compiler that new iteration in ASP.net core libaries will be able to run on Linux and mac based machines without the use of a Windows VM. This will really open up the world of C# development.
With Rosyln being open source, it also means that the IDE itself can also become cross platform, many other IDE's can be used to create .net code, including Sublime and Brackets.
Along this, Microsoft have also backed Xamarien and is built into Visual studio, even including some Xamarin tempaltes on new projects.
Visual studio 2015 preview even comes with Android emulators built directly into the IDE
With all these features together, we can see that Microsoft really wants developers to be able to code in .Net and use and host their code on any device.