I personally like to use it with the todoist app. I've set it up so emails that I "star" automatically get sent to my todoist app. I also have completed todoist items get automatically logged into a spreadsheet for better tracking.
Another one of my favorite integrations, Quire + Gmail, helps me to keep track of deadlines and set schedules. Before, I would contact clients via email and schedule dates with them, with Zapier, I do not need to repeatedly type the dates into my Quire task list.
James Major- Founder of Insurance Panda