This extension will enable you to send push notifications
  from your TYPO3 site straight to your visitors mobile devices. Create an API
  key in PushPro, paste it into your PushPro extension for TYPO3 and your website
  is ready to send push notifications! When your audience visits your website,
  they will now see an opt-in request for push notifications. If they accept,
  you are ready to engage with them. PushPro is a revolutionary way to engage
  with your mobile visitors. Interact directly by sending Push Notifications
  to your subscribers without a mobile app, straight from your website.