I figured I'd just drop a reference here about the Seastar project: http://www.seastar-project.org/
I'm just going to quote from their FAQ:
Seastar is an advanced, open-source C++ framework for high-performance server applications on modern hardware
Seastar futures/promises/continuations (f-p-c) are a subset of reactive programming.
Seastar performance derives from the sharded, cooperative, non-blocking, micro-task scheduled design, and f-p-c are a friendlier way of feeding tasks to the scheduler.
Seastar’s f-p-c do have some optimizations relative to other f-p-c designs. They trade off thread safety, which is unneeded due to the sharded design, for scheduling efficiency, and have a very low memory footprint.
Seastar futures and promises require no locking.
Seastar futures and promises do not allocate memory.
Seastar futures support continuations.
which seems very compatible or in-line with Nim's philosophy (at least what I know of it).
I know Nim provides some of these already; my hope is that some will find additional inspiration in Seastar.