Sometimes you update an app and find that it's not exactly what you wanted. Maybe it's because the new version changes the UI or UX in a way you don't like. Maybe the update is buggy or doesn't work the way the old version did. Whatever the reason, we've all had times where we've updated an app and immediately regretted it. An app called AppDowner has popped up on XDA that can help with those situations.
AppDowner is a simple app that operates on a simple script. The Android OS doesn't let you downgrade your apps to a previous version. You can't just overwrite a new version of an app with an old version. System apps that you can't uninstall have a button that says "Uninstall updates", but that doesn't let you roll back to a specific version. AppDowner uses a script to overcome that. "Since I realized you *can* downgrade your apps (install lower version over actual (higher) version of app) using android feature "pm install -r -d file.apk" yesterday, I got time and wrote small and simple app which does everything for you. Just pick APK and click on Install APK."
You'll need the APK of the app that you want to install. You can pull that from an old ROM backup or you can download it from somewhere online. Be careful where you get your apps. I would recommend pulling the old version yourself. If there are apps that you may want to keep the way they are, copy the APK and store it in a safe place in the case that it's updated and you don't like the update.
AppDowner can really be handy in cases where a developer or company updates an app to a version that doesn't support key functions, too. Sometimes apps get updated to not support rooted devices, with the excuse that it's for security. Sometimes features that you use every day get pulled. Whatever the reason, you can grab AppDowner from the source link below. Keep it on hand because you never know when you may need it.