While it's ecosystem probably does not even match Julia's let alone Python's or the C/FORTRAN-verses, since Nim has been around for almost 20 years and publicly since 2008, there are still a lot of accumulated packages. Some are listed at: https://github.com/ringabout/awesome-nim for really a large (and even so still incomplete!) list of things you might be interested in. Hard to say how well maintained they are. That said, you do probably have to be prepared to do a lot of work yourself and work around compiler limitiations/bugs. Also, binding to C libs is very straightforward with a near trivial FFI.
I suppose it very much depends on the programmer & setting, but like 3 times I've looked for Rust projects similar to Nim ones and found the performance of the Rust quite lacking. Of course, any language that allows you access to assembly makes things ultimately "only" a matter of programmer effort, but the effort to get performance out of Nim seems very competitive in my experience. I've seen at least one ancient 1990s C project be more flexible and much faster in Nim at like 6% the LOC (https://github.com/c-blake/procs for the curious).