Simple DNS Plus is described as 'commercial DNS server product that runs under Microsoft Windows with an emphasis on a simple-to-use GUI. Maintenance of the software appears to have slackened in recent years' and is an app in the Network & Admin category. There are six alternatives to Simple DNS Plus for Linux, Mac, Windows, BSD and Self-Hosted solutions. The best alternative is BIND, which is both free and Open Source. Other great apps like Simple DNS Plus are Unbound (Free, Open Source), PowerDNS (Free, Open Source), djbdns (Free, Open Source) and MaraDNS (Free, Open Source).
Unbound is a validating, recursive, and caching DNS resolver. The C implementation of Unbound is developed and maintained by NLnet Labs. It is based on ideas and algorithms taken from a java prototype developed by Verisign labs, Nominet, Kirei and ep.net.
PowerDNS is a DNS Server that runs on most Unix derivatives. PowerDNS features a large number of different backends ranging from simple BIND style zonefiles to relational databases and load balancing/failover algorithms. A DNS recursor is also included as a separate program.
The djbdns software package is a collection of Domain Name System tools created by Daniel J. Bernstein. It includes software for all the fundamental DNS operations and several DNS debugging tools which administrators use to diagnose misconfigured remote servers.
MaraDNS implements the Domain Name System (DNS), an essential internet service. MaraDNS is open source software: This means that anyone is free to download, use, and modify the program free of charge, as per its license.