What are some alternatives?
When comparing zzzz.io and ClouDNS.net, you can also consider the following products
FreeDNS - Free DNS hosting, lets you fully manage your own domain. Dynamic DNS and Static DNS services available. You may also create hosts off other domains that we host upon the domain owners consent, we have several domains to choose from!
Dyn - Managed DNS, Outsourced DNS & Anycast DNS
Dynu Dynamic DNS - Free dynamic DNS service with powerful features
No-IP - Dynamic DNS and Managed DNS Provider
Duck DNS - Free dynamic DNS hosted on Amazon VPC
NameCoin - Namecoin is a distributed domain name system based on the Bitcoin technology.