App Inventor (version 2) is the newest version of App Inventor. App Inventor is a free system originally from Google for creating applications for mobile devices that use the Android operating system. App Inventor moved to MIT in 2012. Go to http://ai2.appinventor.mit.edu/ to use the new version of App Inventor. For information on the new version of App Inventor see http://www.appinventor.mit.edu/
To get a feel for the types of things you can create with App Inventor see http://gallery.appinventor.mit.edu/#.
In App Inventor 2 you only need a browser (not Internet Explorer) and an internet connection to create apps for Android devices. Chrome, Safari, and FireFox all work. You create the user interface using the Designer and program your app using Blocks. All of your data is stored in the cloud. App Inventor comes with an phone emulator, so you don't even have to have an Android device to test your application. But, if you have an Android device you can download your apps onto it using a wireless network.
You will need a free Google account. If you want to use the phone emulator you will need to install software. If you want to direct connect to your phone you will need to install software and device drivers.
You can upload your app to the Google Play! website - see the following for directions (there is a registration fee of $25 to register as a developer) http://appinventor.mit.edu/explore/ai2/google-play.html
To set-up your computer and phone for App Inventor see Set-up for App Inventor.
Once you finish setting up your computer and phone you can do the tutorials.
To create a project go to http://ai2.appinventor.mit.edu/.
For a reference to all the blocks and user interface components see Reference.
Below you will see links to documents that include a powerpoint introduction to App Inventor, an App Inventor reference, and an user interface reference.