An app that keeps the list of all the apps you've uninstalled and can quickly reinstall them again in case you need it. The idea is to have this for smartphones, but could also be useful on laptops, tablets, etc.
The storage space is running out on your phone, or there are just too many apps and it got really messy and you want to delete those that you haven't used in a while. The problem is - you might need/want to use those apps in the near or not so near future. It would be best if they could stay on your phone, then you wouldn't need to go through the search and installation process again, but.. (see the beginning of the paragraph).
You install the recycling app. It connects to your phone's inbuilt app installation/deletion system. Whenever you are about to uninstall something, the recycling app pops up asking you whether you want to uninstall that particular app totally or whether it should keep it in its memory with the possibility to quickly bring it back.
The recycling app keeps a list of all the apps you chose to potentially resurrect. When you want to do so, you open it and see the list of your uninstalled apps. You see the date when each app was uninstalled and if the same version is still available (and if not, what is available) on google play, apple store, etc. If the app is no longer available to install at all, it might show you similar apps that are available.
When you press "reinstall" the software connects to a certain online source and reinstalls the app from there automatically.
There are apps that function as recycle bins for smartphones, but they are meant to bring back deleted files, not uninstalled apps. Files still take your phone's memory even in the "recycle bin", uninstalled apps, on the other hand - don't, you'd simply need software that could simplify the reinstallation process for you.