How to create one app from multiple Android projects
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Create multiple APKs and remove the Launcher category from activities that you don't need to appear in the app list. For one of the projects there would be a launcher.
But the problem with this approach is that users will have to install all apks or you can make your main apk for that by saying:
"Hey, if you want this feature, go to market and download this app" and point them to apks.
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Change the subproject project to a library project and then refer to it from the main project. Here are the details http://developer.android.com/guide/developing/projects/projects-eclipse.html
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