I've found good longevity for my code, I work in image processing and file organization. I think I would categorize it as tools. I still use a lot of tool like software too, like Notepad, Paint, I use a video processing software called TMPG that I bought about 8 years ago, I occasionally use audio processing software that I bought around the same time, and I use some file processing software that I got a few years ago along with a basic video editor. I think when you find a tool type software you like, you tend to stick with it.

I think the key is to make it as abstract from the system and algorithmic as possible. For example, with image processing, you have a small GUI component and you have a small image type to RGB converter, and the majority of the code is algorithmic RGB array to processed RGB array code. Algorithms don't decay much, but GUIs and file types do, so software that is very tool like and algorithmic has much more longevity as long as the small non algorithmic components are updated occasionally.

Great quote! Most of my experience centers around developing small web/mobile apps where building ten new apps a year is pretty commonplace.

I'll add games to enterprise software as the two places where you'll have the most longevity for your code.