Recently hit on the idea of using Google Forms to track fuel consumption.
For a while I've been thinking that I should figure out what the real MPG is I'm getting from my trusty Mondeo. Writing numbers in a book is sooooo 1990s, I wanted a phone "app" to quickly capture and later process the information.
Google Forms is a simple form design tool available as part of Google Drive. I used it to create a form with date, mileage, amount of fuel and cost of fuel.
When you fill out the form, Google automatically adds an entry line to a spreadsheet My phone browser lets me save the url of the form to my desktop, so I can use it like an "app".
Now I can quickly record the details of each fill-up and keep a running calculation in the Google Sheet behind the scenes.
Next up - weight tracking, running log, ...