Its literally IntelliJ for c# lol. Same base system just tied into the Roslyn compiler chain and using their proprietary .NET debugging system instead of whatever they use for the JVM. And while I still use VS at work on personal projects (in both c# and f#) I've switched fully over to Rider and enjoying the experience a great deal, so anyone used to IntelliJ can get a pretty comparable experience from their IDE right out.