AirDroid is a free Android application that you can use to control your Android device from your desktop, by using a web browser (so it on Linux and any other OS). It can be used to transfer files (upload to the phone or download to your desktop), browse images, quickly sens or read an SMS and many others.
The latest AirDroid 2 beta could only be downloaded by using an invitation, but the apk can now be downloaded by everyone, although it’s not on Google Play just yet. The new version comes with many cool new features such as a new “Find my phone” service, a remote camera feature and finally works over 3G / 4G.