SlimSharp is a custom variant of C# intended to help with some of the worst pain points when using C# for Code Golf. It's something I've had in the back of my head for a while, and I finally took the time today to get it "on paper", at least in a digital sense.
However, so far that's the only way it exists; there is no implementation.
SlimSharp won't keep up with some of the dedicated Code Golf or simple stack-based languages, but it should help reduce byte/character counts relative to other traditional languages.
My goal listing it here is so if I use it in an answer others will be able to verify the program is correct (spot bugs and improvements, etc), even if they have to evaluate the code in their heads, and so we can compare apples-to-apples if others can want to use the same "shortcuts".
Update: There is an implementation now, of sorts, and it is possible to run SlimSharp code. You can even try it on .Net Fiddle.