The newest version of Android(kit kit 4.4) has a lot of cool new things about it, but most notably the coolest thing yet might be the Screencast app developed by Koushik Dutta and the Cyanogenmod Team. This app does have a few prerequisites before use, which include joining the Cyanogenmod Community, and joining the beta, and lastly your phone needs Root access and must be running the latest Cyanogenmod 11 nightly from a couple days ago at least. While Screencast is awesome, the latest from Koush is a similar app called mirror that does pretty much the same thing, but past video playback and sharing it, you can also stream it to airplay.
It's stated that to use this application you first must have Root access just like the Cyanogenmod Screencast app, and with Mirror you also have to be running 4.4.2. While this may be the way it was intended to work, the video I have personally recorded with the app and posted below shows that it can in fact be achieved while still running a nightly build based off of 4.4.1. The app seems to work great, and actually works a little better than the Cyanogenmod screencast app. The one major difference I have noticed is that Mirror seems to playback the video in a "full screen" size frame while the CM Screencast app played video back (for me at least) in a small frame, which made the video a little harder to see.
The intention of both apps is more for development use, but there are obviously a wide variety of applications for an app like this besides development. Using something like mirror to do Android "How to" Tutorials for instance, or even recording playback of a game showing tips and tricks. The possibilities are as limited as you make them, so if you have a rooted device, take the steps needed and grab the app to help test it. Use your imagination. Before doing so you'll have to do a couple things just like with screencast. First you have to join the ClockworkMod community, secondly you'll have to register to become a tester. Once you have done both those things you can hit the Play Store link on the page you registered to become a tester and you can install the app. Once again you have to be rooted to use this app, and you must also be running 4.4.2(no specific ROM required here) according to the description. Koush says he's working on a "non-root" version of the app that can be used via USB tether, and that hopefully he can get it running for Android 4.1 forward. As I have shown above, the app worked for me on a CM 11 nightly build based off of 4.4.1. I have found one bug so far that keeps me from uploading any of my "mirror" recordings to Youtube, but other than that it works awesome! Happy testing everyone!