A free app for Android, by Mundoapp.

With the WAStickerApps, you can easily add funny emojis and emoticons to your chat. You will not need any special skills, just a few taps and you can add a new sticker. If you have already used WhatsApp or another messaging app, then you know how important stickers are. They can convey a lot of emotions, and you will have a hard time finding the right ones. With WAStickerApps, you can choose from thousands of stickers and all are of high quality.

This application is so easy to use that even if you have no idea about how the stickers work, you can still add a new one and it will work perfectly.