I've played around with openkad [1], but never got far enough to create anything meaningful with it. The authors implemented multiple distance metrics for more efficient lookup and distribution; these are described in [2].
TomP2P is mature enough to run in an closed environment (easy network conditions). We are currently working on making it run (relaying, NAT, UPNP) stable in the Internet.
Edit:
Found a list:
https://en.wikipedia.org/wiki/Kademlia#Implementations
Would still like to hear your impressions if you have used any of them.