[SomeGermanGuy]

There is a open source alternative: https://www.nsupdate.info You can roll your own or just use the one they setup. https://github.com/nsupdate-info/nsupdate.info

The project is well maintained and they focus on security.

[stevekemp]

I also setup a Dynamic DNS service, on top of Amazon's Route53, over at https://dhcp.io/

Unfortunately I had to suspend new registrations due to abuse, but the code is open and available on github:

https://github.com/skx/dhcp.io/

[markild]

Dyn is much more a dynamic DNS provider, though that is probably what "most" people know about.