What are some examples of “invented in rust”?

There have been a lot of great “rewrite-in-rust” projects. But I wonder if the rust community has seen some great examples of “invented-in-rust”? In other words, some original software created in rust that does something which no other software does yet?

I am asking this question because in the long run, I feel if something is working already, it is generally hard to justify a rewrite in another language, unless it is out of some kind of passion. But that passion will eventually fade away, and the project will last only if the value it provides really justifies the cost of rewriting.

In the end, I think it is the original work (aka killer app) that drives the language’s popularity.