TeslaUnread provides unread count badges for Nova Launcher Prime and WidgetLocker. It will not work with other desktops or lockscreens.

Unread counts are natively ed for the most popular chat and email apps, such as Hangouts, Whatsapp and all the apps shown in the screenshot.
Additionally on Android 4.3+ TeslaUnread can watch the notification bar to extract unread counts from virtually any app.

Enable TeslaUnread in Nova Launcher or WidgetLocker Settings > Unread Counts, here you may also customize the style of the badge, such as the size and colors.