There are multiple clones named “Felix.” This guide covers the most popular modern version: desktop-cat-felix (Node.js/Electron) available on GitHub.
By default Felix avoids active windows. To let him walk on top: felix the desktop cat
Download the correct file for your OS:
Developed by AdTools (specifically as a "MessageMate"), Felix was designed to promote cat food in the UK and Europe before gaining global popularity. There are multiple clones named “Felix
Install as usual (Windows: run installer; macOS: drag to Applications). felix the desktop cat
Default hotkey: Ctrl + Shift + C (Windows/Linux) or Cmd + Shift + C (macOS) to show/hide Felix.