/etc/resolv.conf is a file that holds the configuration for the local resolution of domain names.
Normally this file is either static or maintained by a local daemon, normally a DHCP daemon.
openresolv will make sure, that multiple processes (eg. dhcpcd, NetworkManager, openvpn)
can write the resolv.conf without overwriting each others changes.

openresolv can generate a combined resolv.conf or a configuration file for a local nameserver
(like unbound, dnsmasq or bind).