A long time ago I was a regular player of the MMO Eve Online, where I acted as an industrial figure, building in-game items for others to use. Like most industrial people I had spreadsheet to work out profit margins on every item I built. This worked well for a while but then one of the APIs my spreadsheet was using changed and it became useless. I still needed the data the spreadsheet gave me and fixing everything manually would have taken few very long boring hours... f*** that!
Instead I decided to build a program, using the item data that is made publicly available by the developer for just these kinds of situations. For simplicity I decided to use WinForms with C# with a hand full of libraries to convert external data types (yaml, xml, json) for use in calculations. I used this for a few months knowing the profit margin for every buildable item in the game.
In the Summer of 2017 I decided that I should give WPF a go and rewrote the majority of the application, adding update checkers and automated data retrieval from the Eve Developer portal so that the program could download and run without manually having to do anything. A lot of the (at that point 2 year) old code was rewritten reducing lines of code to just 28% of the original (2969 to 837) according to Visual Studio's code metrics!