Supported by NLnet Labs and grown from the efforts of several companies including VeriSign, Nominet, and Kirei, Unbound is a validating, caching DNS server and resolver library released to the public as open source (but not an authoritative server). The project began as a Java-based prototype application and was then converted to C for the open source version. Unbound is offered under the BSD license.

The Unbound package 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). manpages and other documentation detail the process of using the library in custom C code, and configuring and launching the daemon (A utility is included to check configuration files for accuracy prior to daemon launch/reatart). An included unbound-host utility provides host lookups based on the unbound resolver.

Support for the server is provided by NLnet Labs, with both a bug tracking system and a mailing list accessible through the Unbound site. According to the developers, the product is developed as a series of modular components, facilitating product extension.

Visit the Unbound project site for detailed documentation.