I've been using CloudHQ for Gmail for a couple of years and it's been a life-changer for me. Among the many apps offered for free, my favourite is the email tracker: I know if and when my email messages are opened and read. No more excuses from the recipients. Other useful apps are the multi-email forward (forward two or more messages in one), the opportunity to save your email in a cloud service like Drive or Dropbox, and the scheduler.  One of the latest apps that I picked immediately is the signature generator: now I'm boasting with a sleek signature at the bottom of my messages. You can add a pic and choose your font and colours.

It's more than 60 free apps at www.cloudhq.net/g_suite but they also offer a paid plan for the more demanding users.