You want to annoy friends and family? Use MouseDown!
When you start this tool, your mouse starts its endless fall. Once it reaches the screens bottom, it teleports to the top and starts its fall again.
Attention: This tool can only be canceled by opening your task manager and killing the executable.
To close it under windows open the task manager with ctrl+shift+esc, switch to the tab processes and find mousedown.exe. Click on end task to stop the endless fall.