Rust is trying to do something far more complicated. Memory-safety enforced by the compiler is a big deal, but it remains to be seen if it's practical. I am really looking forward if rust can make it work, zero-cost memory-safety would really be something amazing to have in a language.
Nim seems to be a nice, low-level, gc-ed and practical language. It doesn't do anything radical, it's pretty small and it does what's already there right. It could become big.
This kinda reminds of linux vs minix. Doesn't mean it will play out the same way, but still.
Rust feels a bit difficult to get into right now, but if they smooth over the impractical bits, it could become the systems language in 10 years. Nimrod feels like a faster version of python or ruby, something a lot of people would like to have.