Android (rooted with Xposed): Some Android apps, like Gmail, show that you have multiple unread notifications -- but they won't tell you how many. Notification Count is an Xposed module for rooted phones that adds a number badge to all your notifications.
You'll need the Xposed framework installed for this tweak, as described in our guide here. Installation is simple: Just open up the Xposed Installer, head to Download, and search for "Notification Count (continued)". Install the module, then activate it and reboot your phone.
By default, it should work with quite a few apps, including Gmail. However, for some apps, you may have to enable a workaround in Notification Count's settings. Find Notification Count in your app drawer, open it up, and tap the Whitelist option. Enable any apps that aren't showing the badges, and (hopefully) they will start working. You can also change the way the badges look, as well as test the module from its settings.