An old type of serial mouse manufactured by Logitech that featured a proprietary protocol. It had a blocky, triangular shape and was extremely popular. It's almost impossible for me to get it supported properly in recent versions of Microsoft Windows or the free X11 servers for Linux.
I remember seeing fancy, limited edition versions of the
mouse at Egghead Software in the mid to late 80's that
featured see through plastic cases and neon colored electronic components within.
They're very reliable and perform quite well, and I think it's a shame that they're no longer in production.