DynDNS Updater is a client app for the DynDNS service. DynDNS offers many services, and some of them are free. I used their free DNS host names with this tool in the past. The service allows you to assign a host name to your IP address. It can be used to redirect traffic for those users who don't have a static IP address. The DynDNS Updater is an application that updates your IP address automatically, so, while you are running it, your host name will be updated at regular intervals, and whenever you get a new IP address. The app sits on the background carrying out checks at regular intervals, and it will change the IP address on file on the servers when it detects a change.
DynDNS Updater allows you to add as many hosts as you have signed up for on DynDNS.com. When you first run the application and add your account login information, all the hosts that you signed up for will be listed. You have to manually check those which you want to be updated automatically. I only use one, and I don't think I have ever had a problem with it. I run several servers on my PC and having a host name allows me to connect to my computer when I am away from it and don't have the means to get my actual IP address.
