Psst! NSD isn't a "resolver" at all. Traditional DNS terminology is tricky to use (given that what is covered by "resolver" in the RFCs does not match how most people see the system as divided up) but something that does not do the resolving part at all is definitely not a resolver.
https://raw.githubusercontent.com/NLnetLabs/unbound/master/d...
https://raw.githubusercontent.com/NLnetLabs/unbound/master/d...
Unbound can also answer queries from data in a text file read into memory at startup, like an authoritative nameserver would; no recursion