gdnsd is an Authoritative-only DNS server which does geographic (or other sorts of) balancing, redirection, weighting, and service-state-conscious failover at the DNS layer.
gdnsd is written in C using libev and pthreads with a focus on high performance, low latency service. It does not offer any form of caching or recursive service, and notably does not support DNSSEC. There's a strong focus on making the code efficient, lean, and resilient. The code has a decent regression testsuite with full branch coverage on the core packet parsing and generation code, and some scripted QA tools for e.g. valgrind validation, clang-analyzer, etc.
The geographically-aware features also support the emerging EDNS Client Subnet draft for receiving more-precise network location information from intermediate shared caches.