I'm looking for some sort of embedded touchscreen device that I can put a c# application on it so a client can use the gui.

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Your best bet would be a Surface Pro or another full-power tablet of that caliber, since it has WiFi, USB, and built-in speakers. If you're writing the app as a Windows 8 Metro App, you can use a Surface RT and be fine, otherwise you have to shell out the bigger bucks for the Pro.

As for installing the app and working with it, one solution is to just connect the device to the network and send the EXE over. If you want to do multiple tests with the app, install Visual Studio Remote Debugger onto the device, then configure Visual Studio on your desktop computer to connect to that device for debugging.

Well as far as Linux goes, you can look in to the PengPod. It's very likely that you'd have to wait a few weeks for one even if you ordered right now. Further, it doesn't have an Ethernet port, though it does have WiFi. Lastly since it's Linux, there's a chance you won't be able to interface with external hardware if there aren't any Linux drivers for them.

This looks like a spambot; a Google search reveals an identical question from August 2012. I am locking this topic, clearing the first post, and suspending the user.