For me the feature that makes Rust stand out is memory safety without garbage collection. It's got all the goodness you'd expect from a modern programming language while giving me basically all the flexibility I could get from writing C or C++. That's a very strong differencing trait, at least for me.

I've never used Nim and I should probably give it a try but it seems that the "garbage collected, parallel oriented" niche is somewhat more cluttered with the likes of Go, the various languages built on top of .Net or the JVM, the lisps, the haskells... Not all target exactly the same use cases but there's a lot of overlap here and it's harder to stand out.