"tomato" is an open-source router firmware package. You can use it to access settings that the manufacturer intentionally hides away, or to set up features like UPnP more easily. Some versions even enable features like a built-in NAS (just bring your own drives), networked printer support, or running a publicly-facing website on your router.

Along with packages like DD-WRT, it's a pretty common modification for a lot of tech-savvy users to make.

Though, to be honest, I'm not entirely certain that a 2011 Belkin router would be compatible with Tomato (probably?).