Pi-hole, AdGuard, Blokada, NetGuard, AdAway, NextDNS, Portmaster, DNSCloak, DNS66, AdGuard Home, NextDNS Manager, ufw KDE, Firewalld, TrackerControl, personalDNSfilter, BLOCK THIS!, AdClear, upribox, NetGenius, DnsAdBlock are some alternatives to RethinkDNS.