Other things called "runkit":

* a PHP module - http://php.net/manual/en/book.runkit.php

* a Swift wrapper for Grand Central Dispatch - https://cocoapods.org/pods/RunKit

* an Objective-J animation library - https://github.com/austinsarner/RunKit

Of course, there are only a finite number of possible names, especially when you limit yourself to names that are brief and meaningful, which makes name collisions almost inevitable. And maybe the above items are all obscure enough that it doesn't matter (I had heard of the first before, due to my past life as a PHP developer, but the other two I only found by searching)