Comment by wizzwizz4

> I think this sort of thing never came to fruition because (aside from it being very hard to make) it would be way too bulky what with having to come in the form of a single app package.

Note that the Android equivalent (custom launchers) doesn't need to, and iOS's implementation (Springboard.app), while more integrated than that, is still more modular than you describe. It's only App Store restrictions that prevent you from having an app that opens other apps. (If all apps cooperate, you can use the custom URL handler mechanism to work around the App Store restrictions.)