AppInventor is a free software for Windows, Mac e Linux and works with Firefox, Safari, Chrome and Internet Explorer 7+ browsers.
It requires Java installed and allows to create native Android apps, so in APK format without programming knowledges.
In the web site you can find the instructions for all 3 OS. About Windows, once downloaded and installed you can find it in the path programsAppinventorcommands-for-Appinventor.
You don’t need to open it, these files just works as support tools for browser and Java application.
Within the Google account you can access the MIT App Inventor Beta, you can start here to create your own projects.
It has a built in emulator and you must have drivers correcly installed and configured for your Android device.
You can create applications visually and in an easy way. There are 4 panels: Palette, Viewer, Component, Properties.
There is also Blocks Editor that allows to combine the various elements and associate actions (if you aren’t able to open you must associate .jnlp extension with Java Web Start, you can find it in ProgramsJavajre7binjavaws.exe).
You can test your apps anytime with the Emulator and the projects can be saved at any moment.
Once finished you can download the APK ready and, in a next step, also publish it inPlay Store.
AppInventor is a basic software but offers various tools to create apps, in the web site you can find docs, tutorials, forums and resources that helps to understand how powerful is the program.