Neko98
Neko98 is a simple desktop toy, featuring a cat that chases your mouse.
This implementation of Neko was written by one "David Harvey" for Windows 98 [as the name clearly shows], but it still runs perfectly fine in the latest versions of Windows.
All the files have been backed up in my Dropbox if you want to try it out. They are completely unmodified, but you can also download Neko98 from the original page, saved to the Wayback Machine in April 18th, 2007.
I also archived the self-installer for Neko98 from here [warning: all other links in the page are busted], which as far as I know nobody else bothered to do. You'll need to enable compatibility mode in order to use it.
A Spanish translation is also available in my Dropbox [no self-installer, though].