Not the oc, but honestly just random shit, like: Linq. Async and await are both in python or rust, but still via anexternal provider afaik (like Tokio). Explicit interface implementation (default trait implementation for the Rust fans)? Nice source generators and what you can fo with them (kinda like aspect programming). Idk if python or js support pattern matching or proper low level or no GC coding. I also enjoy my langauges to have an end of statement character like ; instead of the horrible visual mess python is. Type safety of compile and runtime type checks lol. In C# if you say your module requires int parameter, noone will be able to call it passing None/null/string/date.