What's your magnum opus of Zapier? A zap that's really interesting and/or a real time saver.
For me it's a zap I've built that taps incoming tweets for mentions of Zapier, filters for a bunch of things (did you know, "zapier" means something in Polish) and then consolidates them into a morning digest spreadsheet for me to look at. For added bonus points I've added a path that alerts me on Slack to any tweets that contain a question mark. The idea being that these are people that might need help with Zapier that I can try and convert into customers.
I'm interested to get some inspiration from others!