It is funny how many times you use your full-blown PC as a terminal to another computer (which is quite often not as capable as the terminal computer). If all you need is a remote display and keyboard, a Raspberry PI would be enough. One of the newer Pi 2 boards would be even better.
You could roll your own set of remote access software, but you don’t have to. [Gibbio] has already created a thin client image called RPiTC and recently released version 1.4. The build supports diverse remote protocols including Microsoft Remote Desktop, Citrix, VMWare, and even X3270.
It supports WiFi and VPN. We were a little disappointed that it didn’t seem to have any serial communication programs (in case we wanted to build one into an old TeleType case). Of course, it is just a Linux system so you can install anything you want or need.
If you don’t think it is much of a trick to turn a computer into a thin client, we’ve covered going in the other direction before, too.