The current public release is Unbound 1.0., which includes both a server daemon enabling cached DNS lookups via port communications; and a resolver library that can be linked into developer applications, enabling them to perform or provide DNS lookups directly.
Unbound is being actively developed by NLnet Labs and sponsored by VeriSign, Kirei and Nominet.
See also Unbound: Open Source Caching DNS Server on Datamation.com.