Hopefully it should get better soon-ish, but concurrency (and even parallelism aka threads) unfortunately is probably Nim's weakest point at the moment.

On the good side, compared to go, Nim's interop with C is fully transparent (since Nim uses C as a backend). This means easy access to C libraries, but also makes it very appropriate for embedded targets like microcontrollers (especially with its ARC memory-management system, which is static/deterministic automatic reference counting).