If you have multiple iDevices you can share apps that you purchased from separate apple ID’s. This is good use of the 5 allotted computers that Apple gives you to share your content with. So here’s how to share an app you’ve purchased with a friend. Email the app to your friend (if the file size is small enough) or save it to a flash drive and then copy it to your friend’s computer. Then it must be imported it to his/her iTunes. The last part would be authorizing “your” app on your friend’s computer.
Here is a little instructional on how this is done.
Once you’ve picked the app to share drag it to you desktop.
Next if small enough email it to whom you want to share or save to a flash drive.
now save it to the desktop of the destination computer.
Once it’s saved open iTunes and import the saved file.
Once this is done iTunes will prompt for the Apple ID info of the library it came from. The person that sent the app must enter their password or the app will not import into iTunes.