MIT App Inventor is a fantastic tool for any teacher who would like to have his or her students try their hands at creating a working Android app.
The MIT App Inventor works in your web browser (Chrome is recommended). The only download that is required for App Inventor 2 is the optional emulator. The emulator allows people who don't have Android devices to text their apps on their desktops. If you have an Android device then the emulator is not required and you don't need to worry about installing it. MIT provides excellent support documentation and curriculum for classroom use for new users of App Inventor. Tutorials are available as videos and as written PDFs. A couple of the videos are embedded below.