SKS is an OpenPGP keyserver whose goal is to provide easy to deploy, decentralized, and highly reliable synchronization. That means that a key submitted to one SKS server will quickly be distributed to all key servers, and even wildly out-of-date servers, or servers that experience spotty connectivity, can fully synchronize with rest of the system. You can see SKS in action here:here to see the members of a pool of sks keyservers.
The foundation of SKS is an efficient algorithm for reconciling remote data sets. That algorithm is described in the following papers:
DownloadingThe SKS source and downloads are available from our google code site. You can subscribe to the mailing list here.
DocumentationThere isn't a lot of documentation at present, but you can get a lot of information from the mailing list. You can also look at the man page and the README from the distribution.
An important aspect of this design is that "sks recon" is largely decoupled from "sks db". This means that with a bit of work, it should be possible to augment existing key servers to use the same reconciliation system. Indeed, there isn't much about "sks recon" that is specific to PGP, and so the same code could be extended to apply to other databases.