I created an application (districtmileage.com) that transformed tracking mileage from a painful, manual process via Excel to a streamlined process accessible across devices.
The old process required you to look at a chart made in Excel and manually figuring out the distance between two points. Now a user can just login (if their district has been setup) and the mileages are all prepopulated. Trips are entered through a very minimal interface. At the end of the month the Excel sheet is generated and emailed to them with the click of a button. Then they just print it, sign it and turn it in.
This saved the users literal hours each month and ensured that their mileage was more accurate (which saves the district money as well by eliminating incorrect mileage submissions).