If you are a developer there is a good chance that you have heard about JetBrains, they are a company in the Czech Republic that create a suite of Integrated Development Environments(IDE's) and software development tools.
One of their flagship products: ReSharper, is a plugin for Visual Studio that does refactoring and other various productivity tasks is used by 65 of the top 100 companies in the Forbes 500 list, according to their website.
JetBrains' IDE's are all based upon their IntelliJ IDEA platform, which is programmed in Java, which makes them cross platform compatible, and in my experience it works really well across Windows and Linux.
The announcement is in my opinion it is a very welcomed one, as there will now finally be a real alternative to Visual Studio when it comes to C# development.
JetBrains are known throughout the software development industry for delivering very high quality products, I have personally used their PHPStorm IDE for almost 2 years now and It really does blow alternatives like Zend Studio, Netbeans and Eclipse(if we can even remotely call it an alternative..) out of the water, I have also heard similar praise from Visual Studio users about their plugin called ReSharper.
Up until now there has not really been any real professional alternative to Visual Studio for .NET developers, I think that this will change when Rider is released and have gone through a few iterations and improvements based on consumer feedback.
Cross platform compatibility is also going to be one of Riders strengths, Visual Studio as of now only runs on Windows, but JetBrains' IDEs are as previously mentioned written in Java and offer cross platform compatibility, this does in my own personal experience work really well.
Project Rider is something that will help expand .NET's reach further than before coupled with the recent news about the .NET core being open sourced.
I think it's only a question about time before we will see .NET development being a real viable alternative for Unix based platforms.
Couple that with tight integration with their existing development tools like TeamCity, Upsource and YouTrack they will position themselves as a very lucrative "all in one place"-package for professional development teams in the future.
You can sign up to receive early development builds of the Rider EAP (Early Access Program) on the Rider page on JetBrains' website.