Android App inventor and Etoys are very similiar in their user interface and manipulation of "objects" in terms of allowing a child to build something

You can connect them in an educational sense (or use them side by side in a classroom)  App inventor is for making something that will work on an android tablet or phone.  Etoys is form making something for your desktop computer.  You could "compare" them by trying to make an application in etoys, and making the same application in app inventor.  What is different? Why? (hint, the desktop computer does not have an accelerometer - what is an accelerometer? Excellent classroom discussion ensues....) The concepts are the same, but the implementation and objects at your disposal to create with are different.  The tools compliment each other, and I would also suggest the Alice tool from carnegie mellon as well.  I use all 3 of these tools to teach object oriented programming to elementary, and even middle / high school if they have not been exposed to programming. concepts earlier.  Unfortunately I do not think you will ever have a tool like app inventor for Apple IOS apps due to their stringent control over publishing apps on their platform.  

thanks,
Val Scarlata