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

Unread counts are natively supported 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.

From version TeslaUnread for Nova Launcher 5.1.2:

Improve reliability of Gmail count

Variant
Arch
Version
DPI
(Android 4.1+)
Latest: 4.0.1 on July 16, 2015
(Android 4.4+)
Latest: 5.1.2 on March 29, 2018
All versions
TeslaUnread for Nova Launcher 5.1.2

Version:5.1.2

Uploaded:March 29, 2018 at 9:52PM UTC

File size:1.18 MB

Downloads:25,801

TeslaUnread for Nova Launcher 5.1.1

Version:5.1.1

Uploaded:March 26, 2018 at 8:00PM UTC

File size:1.64 MB

Downloads:1,510

TeslaUnread for Nova Launcher 5.1.0

Version:5.1.0

Uploaded:March 21, 2018 at 7:28PM UTC

File size:1.63 MB

Downloads:1,501

TeslaUnread for Nova Launcher 5.0.8

Version:5.0.8

Uploaded:March 6, 2017 at 9:13PM UTC

File size:1.27 MB

Downloads:21,536

TeslaUnread for Nova Launcher 5.0.7

Version:5.0.7

Uploaded:February 23, 2017 at 8:56PM UTC

File size:1.26 MB

Downloads:2,541

TeslaUnread for Nova Launcher 5.0.7-beta2

Version:5.0.7-beta2

Uploaded:February 20, 2017 at 7:32AM UTC

File size:1.26 MB

Downloads:1,645

TeslaUnread for Nova Launcher 5.0.7-beta1

Version:5.0.7-beta1

Uploaded:February 10, 2017 at 11:57PM UTC

File size:1.26 MB

Downloads:1,836

TeslaUnread for Nova Launcher 5.0.6

Version:5.0.6

Uploaded:March 18, 2016 at 8:09PM UTC

File size:1.29 MB

Downloads:43,734

TeslaUnread for Nova Launcher 5.0.5

Version:5.0.5

Uploaded:March 16, 2016 at 6:38PM UTC

File size:1.29 MB

Downloads:1,498

TeslaUnread for Nova Launcher 5.0.4

Version:5.0.4

Uploaded:March 14, 2016 at 6:46PM UTC

File size:1.29 MB

Downloads:1,406