1.1.1.1 - Free public DNS Resolver, which is fast and secure (encrypt your DNS query), provided by Cloudflare. Useful to bypass your internet provider's DNS blocking, prevent DNS query spying, and to block adult & malware content. It can also be used via API. Note: Just a DNS resolver, not a DNS hoster.
1984.is — Free DNS service with API and lots of other free DNS features included.
cloudns.net — Free DNS hosting up to 1 domain with 50 records
deSEC - Free DNS hosting with API support, designed with security in mind. Runs on open-source software and is supported by SSE.
dns.he.net — Free DNS hosting service with Dynamic DNS Support
Zonomi — Free DNS hosting service with instant DNS propagation. Free plan: 1 DNS zone (domain name) with up to 10 DNS records.
duckdns.org — Free DDNS with up to 5 domains on the free tier. With configuration guides for various setups.
Dynv6.com — Free DDNS service with API support and management of a lot of dns record types (like CNAME, MX, SPF, SRV, TXT and others).
freedns.afraid.org — Free DNS hosting. Also, provide free subdomains based on numerous public user contributed domains. Get free subdomains from the "Subdomains" menu after signing up.
luadns.com — Free DNS hosting, three domains, all features with reasonable limits
namecheap.com — Free DNS. No limit on the number of domains