BitDHT is a LGPL'd general purpose C++ Distributed Hash Table library. It is designed to take hassle out over creating your own DHT. BitDHT is compatible with bitttorrent's DHT and can leverage this network to bootstrap your own personal DHT.
Ermdia is a yet another implementation of Kademlia, which is one of the algorithm of ditributed hash table (DHT), in Erlang. This software is lightweight, fast and easy to understand since an amount of source code is quite small.