It's used in a lot of mission-critical commercial applications which I think is a stronger indicator. It just so happens those aren't open-source. This ranges from mission-critical enterprise software to internal infrastructure tied directly to revenue generation. There is a serious cost to failure there (money, liability, jobs, etc...).

Few software uses these advanced techniques in general, and it isn't so much about Concurrency Kit. There is a barrier to entry as folks have to invest non-trivial amounts of time in learning more about these techniques.

Some open-source examples: http://www.machinekit.io/ https://labs.omniti.com/labs/reconnoiter https://github.com/Litres/turboxsl Aerospike

I'm sure there are others, if there's anything I'm missing, would love to hear.