Dedoimedo posted a short tutorial explaining how to install the Steam gaming platform on Kubuntu

The problem you are facing is as follows. You are quite familiar with all the different flavors of Ubuntu, may their first letter be L, K, X, or vanilla U. Now, you also happen to love Steam, and ever since it was introduced to Linux at the beginning of the year, you have installed it multiple times in your various distros. But never Kubuntu.

Now that you've tried that, too, you realize that Steam is simply missing in the official Kubuntu repositories. You cannot locate it any which way, and you realize that the only way to get it configured is the manual download and install. But we don't want that. We want updates through the repositories. Anyhow, let me show you how you can quickly and easily get Steam running on Kubuntu.

  How to install Steam in Kubuntu - tutorial